A haemodynamic study was conducted in 96 patients with acute myocardial infarction. The method of right heart catheterization at the bedside using the Swan-Ganz floating balloon-tipped catheter is safe and feisible. An elevation of pressure in the pulmonary circulation was revealed in patients with transmural myocardial infarction and in those without clinical signs of heart failure. The pressure elevation is detected the more often the sooner after the onset of infarction the examination is conducted. To evaluate fast pressure changes heart catheterization is essential and cannot be substituted by any other technique of examination Digoxin administration during the acute phase of myocardial infarction fails to produce any significant reduction of the pulmonary circulation pressure, but a prompt reduction of the pulmonary circulation pressure can be achieved by way of Phentolamine infusion. The pulmonary circulation pressure measurements during the acute phase of myocardial infarction are believed to be an indispensable component of examinations for the heart failure therapy.