Inhaled nitric oxide, with a threshold of perhaps only a few parts per million, is a selective pulmonary vasodilator in patients with congenital heart disease and increased pulmonary vascular resistance. Multiple reports suggest that it may be useful in managing postoperative pulmonary hypertension in the cardiac patient, although it is unknown to what extent inhaled nitric oxide can actually reduce morbidity and mortality in this setting. This agent also holds promise for evaluating patients with pulmonary hypertension prior to heart transplantation. Although special care is needed to avoid toxicity related to excess inhaled nitric oxide or nitric dioxide or increased methemoglobin, the risk of complications with inhaled nitric oxide therapy appears to be very low. Inhaled nitric oxide will likely continue to play a significant role in the pre- and postoperative management of patients with congenital heart disease.