The authors relate the results of a clinical and post mortem examination of 12 patients who died for primary pulmonary hypertension (PPH). The clinical, x-ray, echocardiography and electrocardiography data were of the same type in all the patients. Macroscopic studies of the heart also demonstrated similar changes: the heart mass was increased because of hypertrophy of its right parts. At the same time the microscopic picture of small vessels of the lungs turned out fairly diverse. Based on these differences all the cases were divided into 3 groups: veno-occlusive disease, recurrent pulmonary thromboembolism, plexogenic pulmonary arteriopathy. However, certain differences were noted inside the groups either. It is therefore assumed that PPH is a collective notion, uniting different alterations in small pulmonary vessels, that lead to a considerable rise of pressure in the pulmonary artery.