Sildenafil, a phosphodiestrase-5 inhibitor, decreases pulmonary artery pressures (PAP) in patients with idiopathic pulmonary hypertension. There is little data pertaining to its use in unselected patients with idiopathic dilated cardiomyopathy (IDCM). A single oral dose of sildenafil (50 mg) was administered to 11 patients (mean age 44.9 +/- 7 years, 7 males) with IDCM with left ventricular ejection fraction < or = 40% in New York Heart Association class II/III at the time of right heart catheterization. There was a significant decrease in pulmonary artery systolic pressure (from 31.5 +/- 9.7 to 19.0 +/- 5.2 mmHg, p < 0.001) and pulmonary vascular resistance (PVR) (from 3.0 +/- 2.1 to 1.6 +/- 0.8 dyne/s/m(2)/cm(5), p = 0.01) following sildenafil administration. The systemic vascular resistance (SVR) and pulmonary wedge capillary pressure also significantly decreased. No significant differences in heart rate, cardiac index and PVR/SVR ratio were observed. There were no side effects documented. Sildenafil produces favorable vasodilation in both pulmonary and systemic vascular beds with decrease in left ventricular filling pressures, in stable patients with IDCM.