Thirty patients were discharged from hospital after treatment with arterial counterpulsation for acute severe heart failure complicating myocardial infarction. Seventeen patients had been in cardiogenic shock--13 with power failure alone, and 4 with a mechanical complication which required corrective surgery. Thirteen patients were in impending or 'preshock'. The follow-up period after infarction averaged 13-1 months. Results were good in 'preshock' patients, and in shocked patients with a surgically correctable mechanical complication. Results were poor in shocked patients with power failure alone. Counterpulsation has an important supportive role in the treatment of complicated myocardial infarction, provided that intervention is prompt and mechanical complications, if present, are corrected early.