BACKGROUND Since the presence of pulmonary hypertension (PHT) affects the prognosis of the patients, it is important to manage and evaluate PHT. The aim of this study was to compare the hemodynamic effects of inhaled nitroglycerin and iloprost during early postoperative period, in patients with PHT undergoing mitral valve replacement surgery. METHODS One hundred patients with PHT (mean pulmonary artery pressure (MPAP) >25 mmHg at rest), were randomized to receive either inhalation of nitroglycerin (group I; n=50) or iloprost (group II; n=50) in the postoperative period. In both groups, baseline hemodynamic parameters were recorded before the treatment (T(0)). Then, patients in group I received 20 microg.kg(-1) nitroglycerin and those in group II received 2.5 microg.kg(-1) iloprost. The same parameters were recorded immediately after the end of the treatment (T(1)). RESULTS In both study groups MPAP and pulmonary vascular resistance (PVR) were found to be significantly lower at T(1) when compared to that of T(0) period (p<0.05). MPAP and PVR were significantly lower and mean arterial pressure (MAP) was significantly higher in group II when compared to group I at T(1) period (p<0.05). In addition to decreases in PVR and MPAP, iloprost also increased cardiac output (CO)(4.9+/-1.3 vs 5.1+/-0.9, p<0.05) and stroke volume (SV)(48+/-13 vs 56+/-13, p<0.05). CONCLUSIONS Inhaled iloprost and nitroglycerin, both effectively reduce MPAP and PVR without affecting MAP, systemic vascular resistance (SVR) and CO. However, iloprost seems to be a more powerful pulmonary vasodilator, therefore we suggest iloprost inhalation in patients with severe PHT.