Prodromal symptoms and signs of acute myocardial infarction (AMI) and clinical course of unstable angina pectoris were studied in 405 patients with AMI and 165 patients with unstable angina, respectively. The latter group consisted of patients admitted to a coronary care department. The study showed that 81.2% of patients with AMI had had a number of symptoms during the 28-day period preceding the onset of AMI. Neither the patients nor the physicians had given proper and timely attention to them. The hospitalization of patients with unstable angina was, in some cases, effective in preventing development of AMI or in eliminating life-threatening complications of AMI. This resulted in a decline of the AMI mortality.