Twenty-two patients with acute pulmonary embolism were examined by M-mode echocardiography. It was possible to examine both ventricles (with precordial approach) and the right branch of the pulmonary artery (with suprasternal approach) in all patients. With significant pulmonary embolism there occurs dilatation of the right ventricle and of the right branch of the pulmonary artery. The size of the right branch of the pulmonary artery in patients was significantly different from that of healthy volunteers. However, no significant correlation between the degree of anatomic changes (documented by echocardiography) and haemodynamics in the lesser circulation was found. Literature concerning other possibilities of echocardiography in the diagnosis of acute pulmonary embolism is reviewed. Echocardiography represents a suitable complement to diagnostic methods used for the assessment of acute states.