OPINION OF THE COURT
The present appeal involves the degree of certainty required of expert medical testimony to establish, in a medical malpractice case, the causal relation between the harm suffered by a plaintiff-patient and the alleged negligence of a doctor or hospital in failing properly to diagnose and treat the plaintiff's condition in a manner which might have prevented the harm. We believe that such causation may be founded upon expert opinion testimony to the effect that defendant failed to exercise reasonable care in performing an undertaking to render services to a patient which the defendant should recognize as necessary for the other's protection, that this failure increased the risk of physical harm to the patient, and that such harm did in fact result. Because the jury was not properly charged as to this standard, a new trial will be required.
A few minutes before midnight on May 31, 1968, Mrs. Martha S. Hamil telephoned defendant, Bashline Hospital Association, Ltd. (Bashline),1 and told the night supervisor that her husband was suffering from severe chest pains. Mrs. Hamil was advised by the supervisor to bring Mr. Hamil to the hospital. Upon the Hamils' arrival, the Bashline doctor assigned to the emergency unit could not be located but another physician, Dr. J.F. Johnston, was present and ordered an electrocardiogram (EKG) to be taken. Due to a faulty electrical outlet, the EKG machine failed to function. Dr. Johnston then directed that another machine be used, and thereafter left the hospital. A second EKG machine could not be found and, upon receiving no further aid or treatment, Mrs. Hamil transported her husband to the private office of a Dr. Saloom. Mr. Hamil died in Dr. Saloom's office while an EKG was being taken.
In 1969, Martha Hamil, in her capacity as administratrix of the estate of her husband, instituted this action in trespass under the Wrongful Death and Survival Acts. The basis of the complaint was that Bashline failed to employ recognized and available methods of treating decedent's malady, a myocardial infraction. In support of that theory, plaintiff called as its expert medical witness Dr. Cyril Wecht, who outlined the use of beds, oxygen and pain relieving drugs in the treatment of chest pains. Dr. Wecht then expressed his professional opinion that if Bashline had employed the methods and treatment which he had described, Mr. Hamil would have had a 75% chance of surviving the attack he was experiencing when admitted to the hospital. Dr. Wecht also gave it as his opinion that this substantial chance of recovery was terminated by defendant's failure to provide prompt treatment.2 Defendant's expert witness, Dr. John B. Treadway, opined that death was imminent at the time of Hamil's arrival at the hospital and that the patient would have died regardless of any treatment Bashline might have provided. It was Dr. Treadway's opinion, accordingly, that any negligence of the hospital in the circumstances was immaterial.
Following the introduction of all the evidence, the trial court determined that Dr. Wecht's testimony had failed to establish, with the required degree of medical certainty, that the alleged negligence of the defendant was the proximate cause of plaintiff's harm. The court therefore directed a verdict in favor of the defendant. Upon appeal the Superior Court, relying largely on the Restatement (Second) of Torts (hereafter the "Restatement") § 323(a) (1965) concluded that plaintiff had in fact presented a prima facie case of negligence and accordingly reversed the trial court and granted a new trial. See Hamil v. Bashline, 224 Pa.Super. 407, 307 A.2d 57 (1976) — (Bashline I).
Upon retrial, substantially the same testimony was presented by the parties and the case was this time submitted to the jury. Following deliberation, the jury returned a verdict in favor of defendant and, by answers to special interrogatories, expressed its belief that although Bashline had acted in a negligent manner, plaintiff had failed to establish this negligence as a proximate cause of the decedent's death. A new appeal was taken to the Superior Court in which appellant asserted that the trial court's charge to the jury had failed to comply with the holding of Bashline I. Without resolving that issue, a divided Superior Court affirmed the entry of judgment for the defendant on the ground that it was mistaken in ordering the new trial at the time of the first appeal. See Hamil v. Bashline, 243 Pa.Super. 227, 364 A.2d 1366 (1976) — (Bashline II).3 This appeal followed.4
A proper resolution of the present controversy requires that it be viewed in the context of certain well-established principles of tort law.
It is settled in the law that except in rare situations not here involved the mere occurrence of an injury does not prove negligence and that an admittedly negligent act does not necessarily entail liability; rather even when it is established that the defendant breached some duty of care owed the plaintiff, it is incumbent on a plaintiff to establish a causal connection between defendant's conduct and the plaintiff's injury. Stated another way, the defendant's conduct must be shown to have been the proximate cause of plaintiff's injury. Flickinger Estate v. Ritsky, 452 Pa. 69, 305 A.2d 40 (1973); Dornan v. Johnston, 421 Pa. 58, 218 A.2d 808 (1966); Cuthbert v. Philadelphia, 417 Pa. 610, 209 A.2d 261 (1965); Gift v. Palmer, 392 Pa. 628, 141 A.2d 408 (1958); Fries v. Ritter, 381 Pa. 470, 112 A.2d 189 (1955). Proximate cause is a term of art denoting the point at which legal responsibility attaches for the harm to another arising out of some act of defendant, Flickinger Estate v. Ritsky, supra; W. Prosser, Law of Torts, § 41 (4th ed. 1971); and it may be established by evidence that the defendant's negligent act or failure to act was a substantial factor in bringing about the plaintiff's harm. Flickinger Estate v. Ritsky, supra; Whitner v. Lojeski, 437 Pa. 448, 263 A.2d 889 (1970) (plurality opinion); Majors v. Brodhead Hotel, 416 Pa. 265, 205 A.2d 873 (1965); Diakolios v. Sears, Roebuck & Co., 387 Pa. 184, 127 A.2d 603 (1956); Simon v. Hudson Coal Co., 350 Pa. 82, 38 A.2d 259 (1944); Frangis v. Duquesne Light Co., 232 Pa.Super. 420, 335 A.2d 796 (1975). The defendant's negligent conduct may not, however, be found to be a substantial cause where the plaintiff's injury would have been sustained even in the absence of the actor's negligence. Majors v. Brodhead Hotel, supra; DeAngelis v. Burns, 404 Pa. 230, 171 A.2d 762 (1961); Frangis v. Duquesne Light Co., supra; Restatement, § 432.
It is the plaintiff's burden to prove that the harm suffered was due to the conduct of the defendant. As in many other areas of the law, that burden must be sustained by a preponderance of the evidence. Cwiakala v. Paal, 427 Pa. 322, 235 A.2d 145 (1967); Zeman v. Canonsburg Boro, 423 Pa. 450, 223 A.2d 728 (1966); Amon v. Shemaka, 419 Pa. 314, 214 A.2d 238 (1965). Whether in a particular case that standard has been met with respect to the element of causation is normally a question of fact for the jury; the question is to be removed from the jury's consideration only where it is clear that reasonable minds could not differ on the issue. Topelski v. Universal South Side Autos, Inc., 407 Pa. 339, 180 A.2d 414 (1962); Restatement, § 434; W. Prosser, Law of Torts, § 45 (4th ed. 1971); F. Harper and F. James, The Law of Torts, Vol. 2, § 20.2 (1956). In establishing a prima facie case, the plaintiff need not exclude every possible explanation of the accident; it is enough that reasonable minds are able to conclude that the preponderance of the evidence shows defendant's conduct to have been a substantial cause of the harm to plaintiff. Finney v. G.C. Murphy, Co., 406 Pa. 555, 178 A.2d 719 (1962). Thus, once a plaintiff has established facts from which a jury could reasonably conclude that defendant's actions were a substantial factor in bringing about the harm,
". . . `the fact that some other cause concurs with the negligence of the defendant in producing an injury does not relieve the defendant from liability unless he can show that such other cause would have produced the injury independently of his negligence,' Carlson v. A. & P. Corrugated Box Corporation, 364 Pa. 216, 223, 72 A.2d 290, 293 (1950). See Yenchko v. Grontkowski, 385 Pa. 272, 122 A.2d 705 (1956)." Majors v. Brodhead Hotel, supra, 416 Pa. at 273, 205 A.2d at 878.
(C) Expert Testimony
Normally a plaintiff may establish his case of causation with any evidence, direct or circumstantial, which tends to show defendant's actions as the legal cause of his harm. Where, however, the ultimate determinations lie beyond the knowledge or expertise of the average layperson, expert testimony is permitted (and sometimes required) to aid the jury in its understanding of the factors involved and the teaching of the pertinent discipline with respect thereto. Reardon v. Meehan, 424 Pa. 460, 227 A.2d 667 (1967); Weisman v. Sauder Chevrolet Co., 402 Pa. 272, 167 A.2d 308 (1961); Densler v. Metropolitan Edison Co., 235 Pa.Super. 585, 345 A.2d 758 (1975). Although in certain situations involving physical injury, it is possible for a jury reasonably to infer causation from the circumstances of an accident or occurrence, see, e.g., Illingworth v. Pittsburgh Railways Co., 331 Pa. 369, 200 A. 89 (1938); Fenstermaker v. Bodamer, 195 Pa.Super. 436, 171 A.2d 641 (1961), it is generally acknowledged that the complexities of the human body place questions as to the cause of pain or injury beyond the knowledge of the average layperson. See Lambert v. Soltis, 422 Pa. 304, 221 A.2d 173 (1966); Smith v. Yohe, 412 Pa. 94, 194 A.2d 167 (1963). For a plaintiff to make out his cause of action in such a case, therefore, the law requires that expert medical testimony be employed. In addition to its bearing on whether or not the defendant's conduct was negligent, such testimony is needed to establish that the injury in question did, with a reasonable degree of medical certainty, stem from the negligent act alleged. Commonwealth v. Hamilton, 459 Pa. 304, 329 A.2d 212 (1974); Houston v. Cannon-Bowl, Inc., 443 Pa. 383, 278 A.2d 908 (1971). Mr. Justice O'Brien, speaking for the Court in McMahon v. Young, 442 Pa. 484, 276 A.2d 534 (1971), justified this standard for medical opinion testimony as follows:
"The issue is not merely one of semantics. There is a logical reason for the rule. The opinion of a medical expert is evidence. If the fact finder chooses to believe it, he can find as fact what the expert gave as an opinion. For a fact finder to award damages for a particular condition to a plaintiff it must find as a fact that the condition was legally caused by the defendant's conduct. Here, the only evidence offered was that it was `probably' caused, and that is not enough. Perhaps in the world of medicine nothing is absolutely certain. Nevertheless, doctors must make decisions in their own profession every day based on their own expert opinions. Physicians must understand that it is the intent of our law that if the plaintiff's medical expert cannot form an opinion with sufficient certainty so as to make a medical judgment, there is nothing on the record with which a jury can make a decision with sufficient certainty so as to make a legal judgment." 442 Pa. at 486, 276 A.2d at 535.
Bearing in mind the principles briefly set forth above, it may be seen that both parties to this appeal advance established precedent in support of their respective positions.
The plaintiff, relying on the testimony of Dr. Wecht that the negligent acts of the medical personnel at Bashline terminated the decedent's considerable chances for survival, asserts that defendant's failure to provide adequate treatment to her husband was a substantial factor in bringing about his demise and thus defendant is legally liable unless it can be shown that death would have resulted regardless of the action or inaction of defendant. Defendant Bashline, on the other hand, notes that while Dr. Wecht's testimony may have established that an increased risk of harm to the decedent came about as a result of Bashline's negligent conduct, plaintiff nevertheless failed to introduce any testimony that the negligent acts or omissions did, with a reasonable degree of medical certainty, cause decedent's death; therefore, argues defendant, no prima facie case was established, and the case was properly taken from the jury at the first trial. Cf. Idlette v. Tracy, 407 Pa. 278, 180 A.2d 37 (1962). We believe that resolution of this conflict lies in the proper interpretation of Section 323(a) of the Restatement, which has been part of our Pennsylvania law of negligence for a dozen years. DeJesus v. Liberty Mutual Ins. Co., 423 Pa. 198, 223 A.2d 849 (1966).
Section 323 provides:
"§ 323. Negligent Performance of Undertaking to Render Services
One who undertakes, gratuitously or for consideration, to render services to another which he should recognize as necessary for the protection of the other's person or things, is subject to liability to the other for physical harm resulting from his failure to exercise reasonable care to perform his undertaking, if
(a) his failure to exercise such care increases the risk of such harm, or
(b) the harm is suffered because of the other's reliance upon the undertaking."
We agree with the view of the Superior Court majority expressed in Bashline I that the effect of § 323(a) is to relax the degree of certitude normally required of plaintiff's evidence in order to make a case for the jury as to whether a defendant may be held liable for the plaintiff's injuries: Once a plaintiff has introduced evidence that a defendant's negligent act or omission increased the risk of harm to a person in plaintiff's position, and that the harm was in fact sustained, it becomes a question for the jury as to whether or not that increased risk was a substantial factor in producing the harm. Such a conclusion follows from an analysis of the function of Section 323(a).5
Section 323(a) recognizes that a particular class of tort actions, of which the case at bar is an example, differs from those cases normally sounding in tort. Whereas typically a plaintiff alleges that a defendant's act or omission set in motion a force which resulted in harm, the theory of the present case is that the defendant's act or omission failed in a duty to protect against harm from another source. To resolve such a claim a fact-finder must consider not only what did occur, but also what might have occurred, i.e., whether the harm would have resulted from the independent source even if defendant had performed his service in a non-negligent manner.6 Such a determination as to what might have happened necessarily requires a weighing of probabilities. As one authoritative text on tort law observes:
". . . Thus where it appears how an accident happened and also that the victim might have saved himself by taking advantage of a precaution which it has been shown defendant negligently failed to afford, courts have generally let a jury find the failure caused the harm, though it is often a pretty speculative matter whether the precaution would in fact have saved the victim." F. Harper and F. James, The Law of Torts, Vol. 2, § 20.2, at 1113 (1956) (emphasis in original) (footnote omitted).7
Such cases by their very nature elude the degree of certainty one would prefer and upon which the law normally insists before a person may be held liable. Nevertheless, in order that an actor is not completely insulated because of uncertainties as to the consequences of his negligent conduct,8 Section 323(a) tacitly acknowledges this difficulty and permits the issue to go to the jury upon a less than normal threshold of proof. The Fourth Circuit in a case similar to the one at bar, has well stated the justification for this deviation from the normal requirements of proof. In Hicks v. United States, 368 F.2d 626, 632 (4th Cir. 1968), the court stated:
"When a defendant's negligent action or inaction has effectively terminated a person's chance of survival, it does not lie in the defendant's mouth to raise conjectures as to the measure of the chances that he has put beyond the possibility of realization. If there was any substantial possibility of survival and the defendant has destroyed it, he is answerable. Rarely is it possible to demonstrate to an absolute certainty what would have happened in circumstances that the wrongdoer did not allow to come to pass. The law does not in the existing circumstances require the plaintiff to show to a certainty that the patient would have lived had she been hospitalized and operated on promptly."
We agree with this statement of the law and hold that once a plaintiff has demonstrated that defendant's acts or omissions, in a situation to which Section 323(a) applies, have increased the risk of harm to another,9 such evidence furnishes a basis for the fact-finder to go further and find that such increased risk was in turn a substantial factor in bringing about the resultant harm; the necessary proximate cause will have been made out if the jury sees fit to find cause in fact.
In light of our interpretation of Section 323(a), it follows that where medical causation is a factor in a case coming within that Section, it is not necessary that the plaintiff introduce medical evidence — in addition to that already adduced to prove defendant's conduct increased the risk of harm — to establish that the negligence asserted resulted in plaintiff's injury. Rather, once the jury is apprised of the likelihood that defendant's conduct resulted in plaintiff's harm, that Section leaves to the jury, and not the medical expert, the task of balancing probabilities. In so saying we do not intend to undermine the well-established standard of "reasonable degree of medical certainty" as the accepted norm for medical opinions on causation. But we think it would be unreasonable and unrealistic in this type of case to expect a physician to state with a "reasonable degree of medical certainty" what might have happened when the law (Section 323(a)) recognizes the contingencies involved.10 See generally D. Danner and E. Segall, Mediocolegal Causation: A Source of Professional Misunderstanding, 3 Am.J.L. & Med. 303 (1978). Where there is at issue the adequacy of medical services rendered in a fact situation to which Section 323(a) applies, therefore, a prima facie case of liability is established where expert medical testimony is presented to the effect that defendant's conduct did, with a reasonable degree of medical certainty, increase the risk that the harm sustained by plaintiff would occur.11
In light of the discussion in part II hereof it is clear that in the case before us the testimony of Dr. Wecht was sufficient to create a prima facie case of causation and that therefore the lower court was correct in submitting the issue of negligence to the jury under Section 323(a) of the Restatement. It becomes necessary, then, to decide appellant's contention that the trial court erred in its charge to the jury under that Section.12
At the request of Bashline13 and over plaintiff's timely objection, the trial court in its charge to the jury gave the following instruction.
"Unless Mr. Hamil would have died without treatment, his chances for life were not terminated by any failure of the defendants to treat him and such failure cannot be considered a proximate cause of his death."
Our first observation is that although the total charge as given by the court was painstaking, thorough and accurate, we find the particular instruction here challenged to be, at the least, confusing. More serious, however, is the unmistakable implication in this passage that defendant's negligence had to be the sole cause of death in order to bring liability to the defendant when, in fact, liability could attach if the negligence of the defendant were but a substantial factor in bringing about the death. See discussion, supra. In view of the fact that causation vel non was the critical issue in the case,14 we are unable to conclude that this misleading statement of the law, even when read in the context of the unexceptionable charge as a whole, was harmless error or that it did not contribute to the verdict. We conclude that a new trial must be had.
The order of the Superior Court is vacated and the case is remanded to the court of common pleas for a new trial.