75 patients aged under 70 years who had survived acute myocardial infarction complicated by both significant arrhythmias and cardiac failure were followed-up for 1 year in an attempt to identify features which suggest the likelihood of late death or reinfarction. Patients were carefully instructed in the identification and importance of possible prodromal symptoms and the availability of a mobile intensivecare ambulance service and a 24 h hospital control centre. Horizontal ST-segment depression or anginal pain on an exercise test done within 6 weeks of infarction was a useful predictor of late death. Routine twice weekly E.C.G. recordings taken by telephone transmitter at rest and after mild exertion resulted in the identification of significant arrhythmias in only 7 patients. 13 patients (17%) died, 5 of them instantaneously. 4 of the 13 patients and 22 of the 62 survivors reported "prodromal symptoms". Unreported prodromal symptoms were elicited retrospectively in 14 of the 62 survivors and from the relatives of 4 of the 13 patients who died. Thus, 35% of prodromal symptoms were not reported despite intensive patient education and counselling. The incidence of "prodromal symptoms" was no higher in patients who died than in those who did not die.