Abstract
In this report we present a case of primary pulmonary hypertension associated with giant thrombus of the right main pulmonary artery confirmed by autopsy. The patient had had signs and symptoms probably due to slight right heart failure for the past 5 years, then developed exertional dyspnea evidently indicating the occurrence of pulmonary hypertension 2 years ago. Microscopic examination revealed primary pulmonary hypertension with occlusive vascular changes in the muscular pulmonary arteries and arterioles of both lungs. The authors emphasize that, when there is a giant thrombus of the main pulmonary arteries, attention should be paid to the presence of striking vascular changes in the muscular pulmonary arteries and arterioles.