A total of 43 patients were examined: 21 patients with large myocardial infarction (MI) and 22 donors. In MI patients without signs of left ventricular failure, the level of atrial natriuretic factor was higher than that in the controls, which resulted in inhibition of aldosterone production; whereas in those with the signs, it was slightly lower than that in healthy individuals. All the patients with MI were found to have elevated blood plasma levels of cyclic nucleotides and beta 2-microglobulin. Ultrasound application to the heart was demonstrated to normalize secretion of atrial natriuretic factor, to increase plasma cyclic nucleotide levels and to produce no effects on beta 2-microglobulin quantities.