OBJECTIVE--To examine the determinants of case fatality in the first major ischaemic heart disease event (heart attack) after screening. METHODS--Prospective study of 7735 middle aged men drawn from general practices in 24 British towns. RESULTS--During 11.5 years follow up there were 743 major ischaemic heart disease events of which 302 (40.6%) were fatal within 28 days of onset. Previous definite myocardial infarction or stroke and age at time of event were most strongly associated with case fatality. In men with no previous myocardial infarction or stroke, after adjustment for a range of risk factors, antihypertensive treatment (odds ratio (OR) = 1.97, P < 0.05), arrhythmia (OR = 1.93, P = 0.06), increased heart rate (OR = 2.03, P = 0.06), and diabetes (OR = 2.61, P = 0.07) were associated with increased case fatality. High levels of physical activity (OR = 0.53, P < 0.05) and moderate drinking (16-42 units/week) (OR = 0.61, P < 0.05) were associated with lower case fatality, although moderate drinking was not associated with a lower incidence of major ischaemic heart disease events. Current smoking, serum total cholesterol, and systolic blood pressure were not significantly associated with case fatality. In men with previous myocardial infarction or stroke, arrhythmia and to a lesser degree antihypertensive treatment, moderate or heavy drinking, and diabetes were associated with higher case fatality. CONCLUSION--These findings suggest that physical activity may be an important modifiable factor influencing the incidence of ischaemic heart disease and the chance of survival in men without a previous heart attack or stroke. Arrhythmia, increased heart rate, diabetes, and treatment for hypertension are also areas of concern.