To investigate triggers for the occurrence of acute myocardial infarction (AMI) and sudden cardiac death (SCD), we examined the activities immediately before the time of onset in 149 cases of non-fatal AMI and 110 cases of SCD. All of the cases in which death occurred within 24 h from the onset of the underlying cause were considered SCD as long as the cause of death was of cardiac origin or unknown. We calculated the average time which is spent on each activity in the life cycle of Japanese people and estimated the number of incidence of each activity assuming a uniform distribution. Estimated values and actual values were compared. The results were as follows: 1) The incidence of non-fatal AMI and SCD was low while sleeping or resting or doing light work, and was high while using the toilet or doing sport or heavy work. 2) The incidence of SCD was also high even during moderate exertion, such as taking a bath or, walking or cycling, and it was significantly higher than that in the group of non-fatal AMI. 3) The incidence of non-fatal AMI was high while eating or drinking. 4) Many of the patients with SCD had past histories of circulatory diseases, compared to those with non-fatal AMI. This difference in past histories may account for the high incidence of SCD during moderate exertion. (Jpn Circ J 1996; 60: 947-953)