Heart failure (HF) is one of the most frequent consequences of acute myocardial infarction (AMI). The purpose of the study was to establish the most informative indicators of HF functional classes at the stage of sanatorium rehabilitation of Ml patients. The subjects were 509 Ml patients aged 56.1 +/- 0.5 years, undergoing rehabilitation in Saint Petersburg sanatorium Repino. Most of the patients (69%) were male. 433 patients (84.9%) had HF: 222 (51.2%)--functional class (FC) I HF, 166 (38.3%)--FC II HF, 23 (5.3%)--FC III HF, 22 (5%)--FC IV HF. The study established several informative indicators that allow a doctor to determine the FC of HF, such as left ventricle measurements; contraction fraction, determined by means of EchoCG; physical exercise tolerance, determined by means of veloergometry; decrease of working capacity, determined by means of 24-hour ECG monitoring; distance walked by patients during 6-minute walking test.