Peripheral vasodilators nitroglycerin and sodium nitroprusside were given to 29 patients in the treatment of acute circulatory insufficiency (10 of these patients had pulmonary edema) which in most of them was caused by acute myocardial infarction. Diastolic pressure in the pulmonary artery, which was measured by means of a Swan-Ganz balloon catheter, was above 18 mm Hg (18--34 mm Hg) in all patients. Sodium nitroprusside and nitroglycerin given sublingually caused rapid normalization of diastolic pressure in the pulmonary artery and reduction of arterial pressure with no essential changes in the rate of cardiac contractions and cardiac output, which was attended by an improvement in the functional condition of the left ventricle and in the patients' condition. In patients with a low initial cardiac output (less than 2.2 1/min/m2), however, there was a statistically significant increase of this index in the presence of sodium nitroprusside administration. It is advisable to use sodium nitroprusside for long-term treatment of cardiac insufficiency in a low cardiac output, whereas nitroglycerin is a good measure for rapid relief of pulmonary congestion.