Objective: Pulmonary hypertension is a common problem in patients prior to orthotopic heart transplant. This can lead postoperatively to a right-heart-failure of the donor heart ("graft failure"). The pulmonary hemodynamics were routinely measured in the assessment of potential transplant recipients, to estimate if the elevated pulmonary vascular resistance can be decreased with vasodilators or not. Our study compared aerolized Iloprost with three different concentrations of inhaled NO to gauge their effect upon : 1. pulmonary-selective-vasodilation, 2. left ventricular preload, 3. work of the left and right ventricle. Method: The study protocol was approved by the Human Ethics Committee of the Medical Faculty, University of Halle. In routinely performed right-heart-catheterisations we made the additionally needed measurements. The most important of the measured variables were: 1. pulmonary vascular resistance, 2. ratio of pulmonary and systemic vascular resistance (PVR/SVR-Ratio), 3. mean pulmonary arterial pressure, 4. transpulmonary gradient, 5. pulmonary capillary wedge pressure and 6. right- and left-ventricular stroke work index. Results: Iloprost was the more effective pulmonary vascular vasodilator. Furthermore, Iloprost reduced significant left ventricular preload and increased significant stroke volume. Neither of these effects were seen in NO. Both drugs reduced right ventricular work, Iloprost also increased left ventricular work significantly. Discussion: Our study showed that Iloprost is the more effective pulomonary vasodilator. Iloprost increases stroke volume and at the same time decreases left ventricular preload. This can be seen as an indicator for a positive inotropic effect of Iloprost. Therapy with Iloprost is technically easier to perform. In spite of NO inhalation there is no need for intubation to perform Iloprost inhalation. It is possible to use Iloprost in ambulant therapy, so Iloprost inhalation has clinical and practical advantages compared with NO therapy.