Congestive heart failure is one of the major symptoms accompanying acute myocardial infarction (AMI). The study aimed to describe the occurrence, characteristics and prognosis of congestive heart failure in AMI and to compare post-MI patients with and without congestive heart failure. The methods used included baseline characteristics, initial symptoms, electrocardiogram (ECG), mortality during hospitalization and one year follow-up in consecutive patients with AMI admitted to Sahlgrenska Hospital, Göteborg, Sweden. Congestive heart failure was observed in 51% of the cases. Patients with congestive heart failure were older, more frequently had a history of previous cardiovascular disease, and, less frequently had chest pain on admission to hospital. They had a higher occurrence of life-threatening ventricular arrhythmias during initial hospitalization, and their mortality during one year follow-up was 39% as compared to 17% in patients without congestive heart failure (P < 0.001). This difference remained significant when correcting for differences at baseline. Patients with severe congestive heart failure had a one year mortality of 47% vs 31% in patients with moderate congestive heart failure (P < 0.01). Signs and symptoms of congestive heart failure occur in every second patient admitted to hospital due to AMI, and indicate a bad prognosis, which is directly related to the severity of congestive heart failure.