One hundred and twenty-nine Cape Town general practitioner participated in an emergency coronary care project in which one of the main aims was to survey the natural history of acute heart attacks in their practices over a 14-month period. Although the 1-month community mortality rate (28% of 445 patients of all ages and 23% of 356 patients under the age of 70 years) compared favourably with those of other series, the proportion of patients dying before hospitalization was similar to that of other series (approximately two-thirds). Of the 140 deaths in patients of all ages over a 3-month period, 71 (51%) took place before hospitalization or emergency treatment (pretreatment phase); 85 (60,7%) were due to probable or recorded arrhythmias and 47 (33,6%) to pump failure. Of the 71 deaths in the pretreatment phase, 67 (94%) were caused by a probable arrhythmia. Forty-four of the 69 deaths that occurred after treatment and up to 3 months after the onset of symptoms were due to pump failure. Thus, it is concluded that the commonest post-treatment cause of death is pump failure. Conversely, deaths due probable arrhythmias are most common in the absence of medical intervention, when failure deaths are arae. Of the 140 who died, 37% (52 patients) died within 1 hour of the onset of symptoms and 51% (72 patients) within 4 hours after the onset of symptoms. When therapeutic intervention occurred even within the first 2 hours of symptoms, deaths due to probable arrhythmias could be avoided, with only 3 occurring in 188 treated patients. This natural history survey of acute heart attacks is the first of its kind in South Africa.