The clinical course of myocardial infarction (MI), central hemodynamics, cardiac contractility, gas exchange and blood lactate and pyruvate levels were examined in 169 MI patients with hypodynamic circulation. Group 1 was made up of 23 patients whose low cardiac output and heart performance were not accompanied with tachycardia, increased double product and clinical signs of congestive heart failure (CHF), i.e. patients with the hypodynamic syndrome. Group 2 was composed of 146 patients with signs of second- or third-degree CHF (by M. J. Walk's classification). Unlike the patients with the hypodynamic syndrome those with CHF showed reduced cardiac output and heart performance that did not correspond to metabolic requirements of the body as evidenced by increased blood lactate levels and markedly disturbed gas exchange. The patients with the hypodynamic syndrome demonstrated a favorable course of MI and needed no active hemodynamic correction.