(dissenting).
I dissent from the majority opinion. I would hold that there is substantial credible evidence to support the decision that the claimant’s injury was compensable under our workman’s compensation laws.
The applicable statutory definition of “injury” or “personal injury” includes the words “injury by accident arising out of and in the course of the employment.” SDCL 62 — 1—1(2). This court has stated many times that “injury by accident” means that it is sufficient that the injury itself is unlooked for and unexpected and that it is not necessary that the cause of the injury should be untoward and unexpected, occurring without design. King v. Johnson Bros. Construction Co., 1967, 83 S.D. 69, 155 N.W.2d 183; Taylor v. Imperial Casualty & Indemnity Co., 1966, 82 S.D. 298, 144 N.W.2d 856; Tegels v. Western Chevrolet Co., 1965, 81 S.D. 592, 139 N.W.2d 281; Campbell v. City of Chamberlain, 1960, 78 S.D. 245, 100 N.W.2d 707; Tennis v. City of Sturgis, 1953, 75 S.D. 17, 58 N.W.2d 301; Johnson v. La Bolt Oil Co., 1934, 62 S.D. 391, 252 N.W. 869. See generally 1A Larson, Workman’s Compensation Law, § 38.-00. This has also been expressed in Taylor v. Imperial Casualty & Indemnity Co., supra, as follows: “Injuries are caused by accident according to the quality of the *117result rather than the quality of the causes.” 82 S.D. at 304, 144 N.W.2d at 859. The claimant’s heart attack was certainly an unexpected, unlooked for injury which did not result by design. In my opinion, claimant’s heart attack qualifies as an “injury by accident” within the applicable statutory language cited above.
According to the statute, the injury must also arise “out of and in the course of the employment.” This is a clear indication that before an injury is compensable under our workmen’s compensation laws there must be a showing of a causal connection between a claimant’s employment and the injury upon which the claim is based. Edge v. City of Pierre, 1931, 59 S.D. 193, 239 N.W. 191. Establishing the precipitating (contributing) cause of a myocardial infarction is a difficult task. The majority opinion is correct in stating that a determination of whether an employment situation contributed to the injury must rest primarily on the testimony of medical experts because the field is one in which laymen are not qualified by learning or experience to express an opinion. Medical testimony was submitted by deposition in order to establish the causal relationship between the claimant’s employment at Meilman Foods and his heart attack. The medical expert, Dr. Ferrell, in responding to the hypothetical question posed by claimant’s counsel, stated that the claimant’s employment with Meilman Foods was a competent producing cause of the claimant’s myocardial infarction. Dr. Ferrell stated that the exertions resulting from increased line speed and expanded duties were “aggravating causes” and “contributory and/or aggravated factors” in the claimant’s heart attack. On cross-examination, in responding to leading questions, Dr. Ferrell testified that he could not state categorically that the claimant’s heart attack was caused by his employment with Meilman Foods or could be assignable to a specific time or carcass. Dr. Ferrell agreed with counsel on cross-examination that there were many stress situations which could contribute to the atmosphere for the development of heart diseases like that of the claimant. Dr. Ferrell further agreed that the claimant’s employment possibly could be such a contributing factor. The respondent’s counsel then asked, “And in that regard, we are in the range of possibility rather than probability, are we not?” Dr. Ferrell replied, “Well, it’s a fine line, I would say, yes, to your question.” The doctor testified that he based his opinion on the difficulty experienced by the claimant while he was working and that the symptoms of a myocardial infarction increased during the claimant’s period of strenuous exertion. Upon redirect examination, Dr. Ferrell stated that the tension and the strenuous physical exertion experienced in the claimant’s employment was “a contributory or aggravating factor in this fellow’s condition” and that nothing that counsel asked him during cross-examination caused him to change his mind regarding his conclusion as to contribution or aggravation of the heart attack by employment at Meilman Foods.
The majority opinion holds that the expert medical testimony is defective, based partly on the doctor’s statement that the employment was possibly, not probably, a contributing factor. The majority cites Iowa authority for the proposition that this type of testimony, standing alone, is insufficient to establish the requisite causal relationship. I would agree with the majority if the possibility-probability statement was the doctor’s only testimony. That statement, however, was not “standing alone” for the purpose of establishing the causal relationship. Dr. Ferrell stated elsewhere in his testimony that employment tension and stress contributed to and aggravated the claimant’s heart attack. In South Dakota, the essential facts need not be proved by direct evidence but may be established by reasonable inferences from facts known to exist. King v. Johnson Bros. Construction Co., supra; Mehium v. Nunda Cooperative Ass’n, 1952, 74 S.D. 545, 56 N.W.2d 282; Schlichting v. Radke, 1940, 67 S.D. 212, 291 N.W. 585; Edge v. City of Pierre, supra. Also, a compensation award should not be based upon mere possibility or speculation. Harden v. South Dakota Credit Union *118League, Inc., 1973, 87 S.D. 433, 209 N.W.2d 665. The lack of absolute and total certainty in part of the doctor’s testimony should not be taken out of context to spoil the whole effect of his testimony or to nullify his firmly expressed view that the claimant’s employment situation contributed to and aggravated his heart attack. It is my opinion that the doctor’s testimony, taken in its entirety, is not mere speculation or conjecture but rather a substantial medical opinion necessarily equivocal to a small degree because of the inexactness and complexities of medical science.
The majority opinion further holds that the expert medical testimony is defective because the contributing or aggravating cause of the heart attack is not assigned precisely to the two-week period prior to the attack. In my opinion, the majority is taking an overly restrictive view of the requirement that compensable injuries must be assignable to a definite time, place and circumstance. Oviatt v. Oviatt Diary, Inc., 1963, 80 S.D. 83, 119 N.W.2d 649. The claimant’s testimony details his employment history, showing the considerable increases in the speed of the line at the viscera table which resulted in back and chest pains. After a transfer to the final trim line which was purportedly less difficult than the viscera table, there was a change in work tasks which increased the difficulty of the work. The claimant was held responsible for trimming all of the carcass rather than just one portion of the carcass as he was accustomed. This change required claimant to trim standing up and reaching over his head as well as down on his knees. There is testimony that Meilman Foods was slaughtering a grade of beef inferior to the grade slaughtered when claimant had performed the final trim task previously. This required more trimming of fats and foreign matter and more intensive government inspection. The line speed was also faster than claimant had experienced on the final trim task in previous years.
Approximately two or three weeks prior to the claimant’s heart attack, claimant was further required to operate a derailer switch for condemned or retained beef. This function was formerly performed by government meat inspectors. To operate the switch, the claimant had to walk from his work station around a sink which is a distance of about five feet. This task was performed a considerable amount of the time. After this last task was added, the claimant complained to his foreman that the job with its added tasks was just too difficult for him. On December 9, 1974, toward midmorning, the claimant began having back and chest pains again. He complained of these pains to the foreman and asked that he be allowed to go home. The request was refused and the claimant was required to continue to work for the remainder of the day in spite of the fact that the back and chest pains persisted. That evening at around 10:00 o’clock, pain and dizziness forced the claimant into the hospital where a diagnosis of myocardial infarction was subsequently made. In my opinion, these facts and circumstances, which constituted the basis for the expert medical testimony, substantiate the reasonable conclusion made by the deputy director that the heart attack was assignable to a definite time, place and circumstance.
I believe that the time requirement is sufficiently definite if either the cause is reasonably limited in time or the result materializes at an identifiable point. See 1A Larson, Workmen’s Compensation Law, § 39.00. In this case, the precipitating cause is reasonably limited in time to the two or three weeks immediately preceding the claimant’s heart attack. Also, the result certainly materialized on December 9, 1974. The “definite time” requirement of Oviatt can vary to a reasonable extent depending upon the particular fact situation as long as the nexus between cause and effect is not obliterated. Basically, SDCL 62-1 — 1(2) addresses itself to the causal relationship between injury and employment. It is well recognized that this law is entitled to a broad and liberal construction in order to. fully realize its humanitarian purposes. Kraft v. Kolberg Mfg. Co., 1974, 88 S.D. 140, 215 N.W.2d 844; Donovan v. Powers, 1972, 86 S.D. 245, 193 N.W.2d 796; Joffer v. *119Crusy’s Power Brake & Supply, Inc., 1968, 83 S.D. 191, 156 N.W.2d 189. The Oviatt requirements were adopted by the court to use as a tool in the construction and application of the workmen’s compensation law and a restrictive, narrow interpretation of the Oviatt requirements can only lead to a frustration of the purpose of the workmen’s compensation laws.
Additionally, the majority opinion finds that the second Oviatt requirement is lacking; namely, that the heart attack must result from unusual exertion. With this finding, I disagree. The testimony reveals the progressively debilitating effect of the mental and physical strain of increasing exertions required by the claimant’s employment at Meilman Foods. It is clear that the increased difficulty of the tasks required of the claimant mandated unusual exertion. The evidence shows that the addition of the derailer switch task was the “last straw,” making the job entirely too difficult and unusual for the claimant. Even adopting the most restrictive viewpoint, the work became unusual when the claimant was required to continue to work in a state of ill health on December 9, 1974, after he complained of chest and back pains and was not allowed to go home or see a doctor. For the claimant in poor physical condition, the strain involved in terms of its impact on him was no longer the usual one in any sense of the word. Upon the imposition of the additional task of operating the derailer switch and more specifically, on December 9, 1974, the usual exertions for the healthy laborer became transformed into the unusual exertions for the stricken claimant. See 1A Larson, Workmen’s Compensation Law, §§ 38.64(c) and 38.83.
It is generally understood that when we consider the sufficiency of the evidence to support the findings for the claimant made by the deputy director, we must examine the evidence in the light most favorable to the claimant. After doing so, we should disturb the findings only if we can state that they are so palpably erroneous as to be unreasonable. Kraft v. Kolberg Mfg., Co., supra; Joffer v. Crusy’s Power Brake & Supply, Inc., supra; Howe v. Farmers Cooperative Creamery of Madison, 1965, 81 S.D. 207, 132 N.W.2d 844; Elmstrand v. G & G Rug & Furniture Company, 1958, 77 S.D. 152, 87 N.W.2d 606. This I am unable to do. Even though we are not bound by the clearly erroneous rule with regard to the standard of review of the deposition testimony of the expert medical witness, the testimony of the claimant taken together with that of the expert medical witness on the whole record supports the deputy director’s findings and conclusions by substantial, credible evidence. SDCL 1-26-36.
I would reverse the judgment of the trial court and remand the case to the trial court with instructions to have the deputy director enter the proper award of compensation.
I am authorized to state that Justice ZASTROW joins in this dissent.