Prostaglandin E₁ (PGE₁) was used continuously in adults from immediately after induction of anesthesia, during extracorporeal circulation, to the acute phase after open heart surgery. Using blood flow in the toe determined by laser Doppler flowmeter and the temperature difference between periphery and core as indices, the effects of afterload reduction and improvement of peripheral circulation were investigated. Subjects were 17 adults who underwent open heart surgery. PGE₁ was used in 7 patients and not used in 10. In the group using PGE₁, continuous injection of 0.015μg/kg/min of PGE₁ was started immediately after induction of anesthesia and was maintained during extracorporeal circulation until the acute phase after surgery. During extracorporeal circulation, perfusion pressure was kept at 50∼60mmHg and PGE₁ injection was controlled within the range of 0.015∼0.030μg/kg/min. At completion of extracorporeal circulation, the dose was fixed at 0.015μg/kg/min again. The degree of improvement of peripheral circulation was evaluated on the basis of hemodynamics, blood flow in the toe determined by laser Doppler flowmeter and the temperature difference between periphery and core, at induction of anesthesia (before using PGE₁) on completion of extracorporeal circulation, and in the acute phase after surgery. The value of blood flow in the toe determined by laser Doppler flowmeter was significantly higher in the PGE₁ group than in the non-PGE₁ group, from completion of extracorporeal circulation to the acute phase after surgery. Moreover, peripheral temperature was significantly higher in the PGE₁ group than in the non-PGE₁ group at completion of the extracorporeal circulation as well as immediately after surgery, and the temperature difference between periphery and core was significantly smaller. Continuous injection of PGE₁ enabled smooth control of perfusion pressure during extracorporeal circulation. Although there was no significant difference in peripheral vascular and total pulmonary resistance, the coefficients tended to be lower in the PGE₁ group. The use of PGE₁ during open heart surgery seems to be an effective method to improve peripheral circulation.