A follow-up investigation of the prognosis of 381 patients admitted with suspected acute myocardial infarction (AMI) has been carried out in respect of later AMI or death. During hospitalization the patients were divided into groups with particular attention to patients with no demonstrable myocardial infarction but with ischaemic heart disease (non-AMI) and patients with confirmed AMI. All patients were subjected to follow-up for 43 months (range 37-54). The mortality from cardiovascular causes after four years was 26.2% of 130 non-AMI patients and 25.8% of AMI patients. The majority of new infarctions were found in the AMI patients, but with even increase in both groups, 50% occurring within the first 12 months. The groups were studied with regard to earlier manifestations of ischaemic heart disease and heart failure during hospitalization, without any difference being observed. Due to the poor prognosis the question is raised whether non-AMI patients as a group should be offered prophylactic therapy.