Nitric Oxide (NO) is an endogenous mediator produced from the vascular endothelium. The NO is a powerful vasodilator and is used in intensive care in inhaled way as selective pulmonary vasodilator (iNO). NO decreases the RVP, the shunt effect and improves the oxygenation by optimization of ventilation-perfusion ratio. The short lifetime of iNO (6sec approximately) allows a fast metabolism without inducing any undesirable effects such as the systemic hypotension.