OBJECTIVE To assess the risk of death from heart disease after Hodgkin's disease therapy. METHODS Retrospective study comparing treated patients with a matched general population. METHODS Referral center. METHODS A total of 2232 consecutive Hodgkin's disease patients treated from 1960 through 1991. Follow-up averaged 9.5 years. METHODS Relative risks (RRs), the ratio of the observed to the expected cases with 95% confidence intervals (CIs), chi tests for trends, and Kaplan-Meier actuarial risks. RESULTS Of the 2232 patients, 88 (3.9%) died of heart disease, 55 from acute myocardial infarction and 33 from other cardiac diseases, including congestive heart failure, radiation pericarditis or pancarditis, cardiomyopathy, or valvular heart disease. The RR for cardiac death was 3.1 (CI, 2.4 to 3.7). Mediastinal radiation of 30 Gy or less (n = 385 patients) did not increase risk; above 30 Gy (n = 1830), RR was 3.5 (CI, 2.7 to 4.3). Blocking to limit cardiac exposure reduced the RR for other cardiac diseases from 5.3 (CI, 3.1 to 7.5) to 1.4 (CI, 0.6 to 2.9), but not acute myocardial infarction (RR, 3.7 vs 3.4). The RRs increased with duration after treatment (trend in acute myocardial infarction, P = .02; in other cardiac diseases, P = .004). The RR for acute myocardial infarction was highest after irradiation before 20 years of age and decreased with increasing age at treatment (P < .0001 for trend). CONCLUSIONS Mediastinal irradiation for Hodgkin's disease increases the risk of subsequent death from heart disease. Risk increased with high mediastinal doses, minimal protective cardiac blocking, young age at irradiation, and increasing duration of follow-up.