In 6 patients affected by coronary artery disease, undergoing right and left heart catheterization, under resting conditions and after intravenous injection of 100 mg trapidil, the following haemodynamic parameters were recorded: heart rate, cardiac output, right atrial pressure, pulmonary artery pressure, capillary wedge pressure, aortic and left ventricular pressure. Furthermore, left ventricular angiography was performed before and after trapidil administration and the end-diastolic and systolic images were digitized on a computer. After administration of trapidil, an increase of the heart rate, a significant decrease of the systemic systolic pressure and of the pulmonary artery pressure together with a reduction of the systemic and pulmonary vascular resistances were noticed. Even end-diastolic volume and end-diastolic pressure significantly decreased. The results point out a remarkable effect of trapidil on the peripheral and pulmonary circulation.