The classic studies of daily activity prior to myocardial infarction onset conducted by Master in the 1960s failed to show a consistent relationship between any particular activity and disease onset. However, they were conducted at a time when less was known of the pathophysiology of myocardial infarction, when there was less understanding of the effect of daily activities on physiologic processes likely to lead to myocardial infarction onset, and when epidemiologic methods were less well developed than at present. Certain activities now of considerable interest, such as wake time, time of assuming the upright posture, eating and taking of medications, were not examined and those that were examined such as walking and heavy exertion, were evaluated without reference to control exposure. In addition, modern enzymatic methods of confirmation of the diagnosis of acute myocardial infarction were not utilized. Despite these deficiencies, the studies of Master provide the foundation for the hypothesis that the onset of myocardial infarction is almost always a random event.