delivered the opinion of the court:
Claimant, Delores Cognato, filed an application for adjustment of claim pursuant to the Workers’ Compensation Act (Act) (111. Rev. Stat. 1983, ch. 48, par. 138.1 et seq.). She sought compensation for the death of her husband, Samuel Cognato (decedent), who died from a ruptured myocardial infarction, which claimant alleged occurred while Samuel worked for employer, Lucca Packing Company. After a hearing, the arbitrator awarded benefits to claimant. The Industrial Commission (Commission), with one commissioner dissenting, reversed the arbitrator’s decision. Upon review, the circuit court confirmed the Commission’s decision. This appeal followed.
On June 26, 1992, an opinion of this court was filed. A petition for rehearing was filed by the respondent, the petition was granted pursuant to Supreme Court Rule 367 (134 Ill. 2d R. 367) and an answer was filed by the petitioner.
On appeal, claimant raised two issues, namely, that the Commission’s finding that Samuel’s death did not arise out of and in the *52course of his employment was against the manifest weight of the evidence; and that the Commission’s finding on the causation issue is contrary to the manifest weight of the evidence.
Decedent was employed as a sausage maker by employer. On January 22, 1985, decedent tripped and fell while carrying a box of meat weighing between 50 and 75 pounds. He was transported by ambulance to Rush-Presbyterian-St. Luke’s Medical Center, at which time cardio-pulmonary resuscitation was attempted. Decedent was pronounced dead upon arrival at 1:48 p.m. The death certificate states that the immediate cause of death was pericardial tam-ponade due to a ruptured myocardial infarction. A postmortem examination showed evidence of severe coronary arteriosclerosis and the myocardial infarction with rupture.
In the morning of January 22, 1985, Steve Magrini, another employee of the employer, stated that decedent had prepared batches of sausage from 6:15 a.m. until 10:30 a.m. Barrels of meat were brought into the sausage room where Magrini and decedent lifted the meat from the barrels with pitchforks. A barrel contains 150 pounds of different kinds of meat which are later converted into sausage. After making several batches of sausage, decedent and Magrini began grinding beef. At approximately 12:15 p.m., decedent left and went downstairs with Patrick Joslin.
Patrick Joslin worked with decedent and shared the same job responsibilities, which included making sausage, stocking shelves and loading and unloading trucks. Decedent was primarily a sausage maker, which involves running a sausage-making machine operated by a knee pedal. On January 22, 1985, a delivery consisting of 12 cases of beef tenderloin arrived at the loading dock. At approximately 12:25 p.m., Joslin and decedent began unloading the boxes, which weighed between 50 and 75 pounds. Joslin saw decedent unload five or six boxes of the meat. Shortly thereafter while carrying another case of meat, decedent tripped on a sewer and fell forward into a table. Joslin also observed that during the fall, decedent struck his head on a shelf and “just laid there.” On the day of decedent’s death, the temperature reached a high of 20 degrees Fahrenheit and a low of 11 degrees Fahrenheit, the average temperature measuring at 16 degrees Fahrenheit.
The employer’s president, Fred Nottoli, testified that employees Steve Magrini and Pat Joslin were responsible for unloading the trucks when the meat shipments arrived. On some occasions, however, decedent would assist in the unloading. On January 22, 1985, Nottoli observed the bluish color of decedent’s hand when the latter *53came into the office to show Nottoli his right hand. Nottoli saw the decedent’s hand around 10 a.m. and suggested that he see a doctor or go to the hospital. Decedent did not leave, however, and continued to work. Nottoli further testified that the temperature inside the plant was in the neighborhood of 50 to 60 degrees Fahrenheit.
Claimant stated that decedent was 56 years old, stood about 5 feet 10 inches and weighed 228 pounds at the time of his death. He smoked one-half a pack of cigarettes a day for an unspecified number of years. Claimant and decedent owned a two-story building in Berwyn, Illinois, which had a frozen pipe problem during the weekend preceding her husband’s death.
Decedent and his son went to the . building to work on the plumbing on the Monday, January 21, 1985, and possibly on Sunday, January 20, 1985. On Monday, January 21, decedent left for the building at 4 p.m. and returned home around 6:30 p.m.
Dr. Nathaniel Greenberg, board certified in internal medicine, and Dr. Michael Lesch, a board-certified cardiologist, testified before the arbitrator. Their testimony was presented with respect to the issue of whether the decedent sustained accidental injuries arising out of and in the course of his employment or that a causal relationship existed between the incident of January 22, 1985, and his death. Upon review of the medical records, Dr. Greenberg opined that the unloading and carrying of the heavy boxes of meat in the cold environment put an excessive strain on the previously infarcted heart, causing the rupture which led to the decedent’s collapse and death. He further testified that the infarcted heart muscle is at its weakest between 5 to 12 days following the infarct and for this reason, individuals who have suffered from a myocardial infarction are urged to stay at rest during the critical period. He also stated that heavy work in a cold environment “is just the sort of circumstance that leads to rupture.” Dr. Greenberg disputed the employer’s position that the decedent’s death could have been caused by repair work on frozen pipes performed the Sunday preceding his death. He further stated that exertion markedly increases the likelihood of a rupture.
Dr. Lesch testified that he saw between three to five “infarct” patients per week and had written extensively on the subject of myocardial infarction. Dr. Lesch opined that there was no relationship between the decedent’s employment and the post-myocardial infarction rupture. His reasons for that opinion were basically threefold. First, Dr. Lesch reasoned that there was no causal connection because there is no data to show that effort affects the inci*54dence of post-myocardial infarction ruptures. Next, Dr. Lesch stated that the incidence of rupture does not vary according to the seasons of the year or geographical regions; hence, he concluded that temperature was not a factor. Finally, Dr. Lesch opined that effort does not affect the incidence of rupture because of recent trends in treatment of myocardial infarction patients with exercise.
He further testified that decedent’s death could be explained by two alternative scenarios that would be consistent with the autopsy report. Under the first, decedent could have ruptured his heart, and then he collapsed. Under the second, decedent could have collapsed from a cardiac arrest, which necessitated the administration of cardiopulmonary resusitation, which, in turn, caused the rupture. According to Dr. Lesch, either scenario could have occurred.
Dr. Lesch also indicated that 99.9% of the cases of myocardial infarction are caused by coronary arteriosclerosis and complications thereof, which are in turn associated with such factors as high cholesterol, smoking, obesity, hypertension, diabetes, and a sedentary lifestyle. He further stated that from his research there was no data whatsoever to show that the external factors such as exertion, exercise or cold temperature played any part in causing a post-myocardial infarction rupture.
As found by the Commission, Dr. Lesch disagreed with the opinion of petitioner’s expert, Dr. Greenberg, who believed the physical stress of lifting heavy boxes and the cold environment put an excessive strain on decedent’s previously infarcted heart, causing the rupture and subsequent collapse and death.
The Commission adopted the findings and opinions of Dr. Lesch and found that “Decedent’s collapse from a fatal heart rupture was unrelated to exertion or temperature and that in any case, Decedent’s physical exertion on January 22, 1985 was minimal and not beyond his regular duties.”
The arbitrator ruled in favor of the petitioner. The arbitrator’s decision noted Dr. Lesch admitted that he would never allow an individual who had suffered a myocardial infarction to lift boxes weighing 50 to 100 pounds, and that strenuous activity could aggravate that condition. On review, however, the Commission relied on Dr. Lesch’s testimony in reversing the arbitrator’s decision. The Commission concluded that the decedent’s heart rupture was unrelated to exertion or temperature and that the decedent’s physical exertion on the day of his death was minimal and not beyond his regular duties.
*55 It is axiomatic that the Commission’s determination as to causation will not be disturbed on review unless it is against the manifest weight of the evidence. (Horath v. Industrial Comm’n (1983), 96 Ill. 2d 349, 356, 449 N.E.2d 1345, 1348.) Where an employee suffers a heart attack which produces disability or death, the disability or death is compensable under the Act if the heart attack is work related. (Wheelan Funeral Home v. Industrial Comm’n (1991), 208 Ill. App. 3d 832, 836, 567 N.E.2d 662, 665.) Compensation is not precluded by the fact that the employee may have suffered from a preexisting heart disease. (Johns-Manville Products Corp. v. Industrial Comm’n (1979), 78 Ill. 2d 171, 177, 399 N.E.2d 606, 609.) Where a preexisting heart disease is evident, recovery turns upon whether the heart attack was a product of the heart disease and the employment combined, or the heart disease alone. (Tyrrell v. Municipal Employees Annuity & Benefit Fund (1975), 32 Ill. App. 3d 91, 96, 336 N.E.2d 97, 102.) A claimant is not required to prove that the employment was the sole or principal cause, but only that the employment was a causative factor. Wheelan Funeral Home, 208 Ill. App. 3d at 836, 567 N.E.2d at 665.
If work-related stress aggravates or accelerates the heart condition so as to cause a heart attack, the heart attack is an accidental occurrence that arises out of and in the course of employment unless the employee’s condition was so poor that any activity would constitute an overexertion. Johns-Manville Products Corp., 78 Ill. 2d at 177, 399 N.E.2d at 610.
It is the Commission’s province to judge the credibility of witnesses, to draw reasonable inferences from the testimony and to determine what weight the testimony is to be given. (Paganelis v. Industrial Comm’n (1989), 132 Ill. 2d 468, 483, 548 N.E.2d 1033, 1040.) Further, it is the Commission’s province to resolve conflicts in medical evidence. (Amoco Oil Co. v. Industrial Comm’n (1991), 218 Ill. App. 3d 737, 747, 578 N.E.2d 1043, 1050.) The Commission’s decision on a question of fact will not be disturbed unless it is contrary to the manifest weight of the evidence. Paganelis, 132 Ill. 2d at 484, 548 N.E.2d at 1040.
Where the inferences drawn by the Commission are reasonable, a court of review will not discard them merely because other inferences could be drawn from the evidence. (Warren v. Industrial Comm’n (1975), 61 Ill. 2d 373, 376, 335 N.E.2d 488, 490.) It is not the prerogative of the reviewing court to reweigh the evidence and substitute its judgment for that of the Commission. A reviewing court is not the trier of fact. Likewise, it is for the Commission to *56decide which of two conflicting opinions should be accepted. Material Service Corp. v. Industrial Comm’n (1983), 97 Ill. 2d 382, 387, 454 N.E.2d 655, 657.
Claimant argues that the Commission erred in relying on Dr. Lesch’s opinion in determining that no causal connection existed. The employer contends that Dr. Lesch’s testimony was not comprised by the concessions he made regarding the treatment of myocardial infarction in patients immediately following the disease’s onset.
Dr. Lesch testified there was no causal connection because there was no data to show that effort affects the incidence of post-myocardial infarction ruptures, the incidence of ruptures does not vary according to the seasons of the year or geographical region, and that effort does not affect the incidence of rupture.
Both medical experts agreed there was no relationship between the work and the myocardial infarction because the myocardial infarction predated the work.
Dr. Lesch testified “there is no evidence anywhere in the medical literature that correlates rupture to either physical exertion or temperature.” He further testified “that rupture is a natural consequence of myocardial infarction in 10 to 15 percent who die of myocardial infarction, and that this occurs because of factors which we are unaware of, and to which we can attribute no specific cause and effect relationship,” and “the rupture was the natural evolutionary cause of this man’s heart attack and was independent of external factors.”
The subject of myocardial infarctions and ruptures is not of common knowledge and requires expert opinion with respect to causal connection in cases such as the one before us. The Commission believed Dr. Lesch, board certified in cardiology. The Commission found that the petitioner failed to prove that decedent sustained accidental injuries arising out of and in the course of his employment on January 22, 1985, or that a causal relationship existed between the incident and decedent’s death. The decision of the Commission was not against the manifest weight of the evidence.
Accordingly, we affirm the judgment of the circuit court.
Affirmed.
EGAN and STOUDER, JJ., concur.