BACKGROUND: Increasing coronary perfusion pressure with phenylephrine is important treatment strategies for right ventricular dysfunction caused by pulmonary hypertension. We compared the effects of phenylephrine on systemic and pulmonary hemondynamics in patients with and without pulmonary hypertension. METHODS: Twenty patients undergoing a valvular replacement were divided into two groups according to pulmonary artery pressure (PAP): control group (mean PAP < 25 mmHg, n = 9) or pulmonary hypertension group (mean PAP > 25 mmHg, n = 11). When systolic blood pressure decreased below 100 mmHg after the induction of anesthesia, phenylephrine was infused to raise systolic blood pressure up to 30% and 50% over baseline. Hemodynamic variables were measured at each time. RESULTS: Phenylephrine failed to raise systolic blood pressure up to 50% above baseline in more than half of the patients with pulmonary hypertension in contrast to successful increases in all patients without pulmonary hypertension. However, the ratio of PAP to systolic blood pressure was significantly reduced in patients whose systolic blood pressure was successfully increased up to 50% over baseline in the pulmonary hypertension group whereas the PAP concomitantly increased as systolic blood pressure was increased in the control group. CONCLUSIONS: Phenylephrine couldn't increase systolic blood pressure in some patients with pulmonary hypertension unlike in control group and it seemed to occur more often in patients with greater the ratio of PAP to systolic blood pressure. The baseline systemic vascular resistance index was high and cardiacoutput was low in the pulmonary hypertension group and these conditions seemed to restrict the effect of phenylephrine.