The role of arterial counterpulsation was sought in 100 patients with severe refractory cardiac failure complicating myocardial infarction. Seventy-four were in shock and 26 were not. Average duration of counterpulsation was 7.0 days. Hospital survival was 34 per cent (25/74) in shock (predicted less than 10%) and 65 per cent in patients who were not in shock (predicted less than 50%). Survival at 4 years was 10 +/- 4 per cent in shock and 37 +/- 11 per cent in patients not in shock; functional status was class 1 or 2 in 5 of 9 patients in shock and in 8 of 12 survivors not in shock. Results were best when counterpulsation was started early after onset of symptoms, when ischaemic pain was still present, or when a mechanical defect was corrected surgically. Early coronary artery bypass surgery performed alone in 9 patients did not influence survival or functional status. Complications of counterpulsation occurred in 17 patients in shock and in 2 patients not in shock, all but 6 on the first day; none directly caused death. Counterpulsation is an effective and safe adjunct to medical treatment of complicated infarction provided the intervention is prompt.