BACKGROUND: The underlying risk of death in the absence of treatment after a myocardial infarction (MI) is poorly documented. METHODS: Analysis of 23 published studies in which 14 211 patients were followed prospectively after MI; 6817 deaths were recorded. We restricted the analysis to studies in which follow-up was completed by 1980 to quantify the underlying risk in the absence of effective treatments. RESULTS: After a first MI, on average, 23% of patients died before reaching the hospital and another 13% died during hospital admission; these rates increased with age. After hospital discharge cardiovascular mortality was approximately 10% in the first year and 5% per year thereafter, rates that were unrelated to age or sex. The yearly death rate of 5% persisted indefinitely; after 15 years, cumulative cardiovascular mortality was 70%. After a subsequent MI, 33% of patients died before reaching the hospital, and 20% died in hospital. After discharge, cardiovascular mortality was approximately 20% in the first year and 10% per year thereafter, rates again unrelated to age and sex. Approximately a third of all heart disease deaths occurred minutes after the first MI, a sixth during the first hospitalization, and half after a subsequent MI, which could occur many years after the first. CONCLUSIONS: In persons with a history of MI, cardiovascular mortality in the absence of treatment is high-5% per year after a first MI and 10% per year after a subsequent MI, persisting for many years and probably for the rest of a person's life. The high mortality rate emphasizes the need to ensure that everyone who has had an MI, even years previously, receives effective preventive treatment.