Incidence of sudden death and arrhythmia pattern were studied using ambulatory monitoring in 40 patients resuscitated<24 hours (n = 26, Group I) or 4–12 weeks (n = 14, Group II) after myocardial infarction. Forty patients with myocardial infarction and no resuscitation served as controls (Group III). Ambulatory ECGs were recorded with an average of 2 months (Recording 1) and 28 months (Recording 2) after myocardial infarction. Incidence of sudden death was significantly higher in Group II (43%) than in Group I (15%) or Group III (8%) (p<0.01). In Recording 1, there were no significant differences in the incidence of premature ventricular beats and complex arrhythmias (couplets or salvos) between survivors and sudden death patients in Groups I, II and III, whereas in Recording 2 the mean incidence of premature ventricular beats and complex arrhythmias was significantly higher in survivors in Group II than in Group I or Group III (p<0.05). In addition, in survivors in Group II, incidence of premature ventricular beats and complex arrhythmias was significantly higher in Recording 2 than in Recording 1 (p<0.05). Our data show that the risk of sudden death is high in patients with cardiac arrest 4–12 weeks after myocardial infarction. Repeated studies using ambulatory monitoring are helpful in estimating the risk of sudden death in patients with myocardial infarction and cardiac arr