Background Deaths caused by substance abuse, circulatory disorders, and external causes such as suicide, homicide, and accidents are more likely to occur during the first week of the month than the last week of the preceding month. The purpose of this report is to determine if death caused by acute myocardial infarction occurs more often in the first 7 days of the month than in the last 7 days of the preceding month. Methods and Results This study used computerized death records for Washington state from 1988 to 1997. There were 401,314 deaths, of which 33,436 (8.3%) had an underlying cause of acute myocardial infarction. The week of the month during which death occurred was defined as occurring during the first 7 days of the month or the last 7 days of the preceding month. R, the ratio of the number of deaths during the first 7 days of the month to the number of deaths in the last 7 days of the preceding month multiplied by 100, was calculated, as were 95% confidence intervals. R values for other cardiac causes and substance abuse–related causes were also calculated. Deaths caused by acute myocardial infarction occurred more often in the first week of the month than in the last week of the previous month (R = 104.4, 95% confidence interval 101.7-107.8). This pattern of death was most apparent for individuals ≥75 years of age (R = 107.3, 95% confidence interval 102.1-111.1) and was not evident for other cardiac causes, including congestive heart failure or myocardial ischemia. By comparison, substance abuse–related deaths occurred much more frequently during the first week of the month (R = 117.6, 95% confidence interval 110.0-125.8). Conclusions This pattern of death for acute myocardial infarction may be in part caused by stressful events associated with the first week of the month. (Am Heart J 2000;140:196-9.)