Normal pulmonary circulation is a high-flow, low-resistance circuit capable of accommodating the entire right ventricular output at one fifth the pressure of the systemic circulation level. The thin-walled right ventricle functions primarily as a flow-generator pump and is particularly sensitive to increases in its after load. Increased pulmonary artery pressure and pulmonary vascular resistance characterize pulmonary hypertension. Pulmonary hypertension is present when the systolic and mean pressures in the pulmonary arteries exceed 30 and 20 mm Hg, respectively. Pulmonary hypertension is of primary and secondary forms. Primary pulmonary hypertension (PPH) is a disease of unknown etiology, whereas secondary pulmonary arterial hypertension is due to either intrinsic parenchymal disease of the lung or disease extrinsic to the lung. Unfortunately, PPH is a progressive disease that has no cure. Although spontaneous remission is possible, this is exceptionally rare. Few individuals with PPH respond to the acute administration of vasodilators and/or anticoagulants.