Ventricle myocardium of 16 patients who had died from acute thromboembolism (TE) of the pulmonary arteries was studied. The most important factor in the development of myocardial alterations is the degree of a vascular occlusion by the thrombus. Chronic lung and heart diseases as well as patient age may considerably aggravate the structural changes of the cardiomyocytes. Relatively low activity of catabolic enzymes in the myocardium of patients with TE correlates with a small size of embolic damage, the presence of chronic lung and heart diseases and with advanced age.