Low systemic vascular resistance (SVR) hypotension concomitant with pulmonary hypertension (PH) is difficult to manage postoperatively because they are often catecholamine-resistant. So, we applied arginine vasopressin (AVP), which is a potent vasoconstrictor in a specific condition, for post-cardiotomy refractory low SVR hypotension concomitant with PH. We treated nine cases of postoperative refractory vasodilatory hypotension concomitant with PH even after conventional treatment that included nitric oxide inhalation and/or intraaortic balloon pump. AVP was administrated with 0.05 approximately 0.1 U/min intravenously. After AVP administration, the mean systemic arterial pressure increased from 47.3+/-9.5 to 76.5+/-12.2 mmHg (P<0.01) and SVR increased from 488.1+/-92.7 to 1188+/-87 dynes x s x cm(-5) (P<0.01). Fortunately, even though the cardiac index decreased, it remained in a normal range. Alteration in the PVR was not significant, but the Pp/Ps became somewhat lower (0.66+/-0.2 to 0.47+/-0.16, P<0.01). AVP increased the urine output and improved oxygenation. AVP improved systemic circulation (increased systemic blood pressure with maintaining cardiac output) without deterioration of pulmonary hypertension. AVP is an ideal drug for treating refractory low SVR hypotension concomitant with PH. But its indication must be limited.