Two cases of very difficult weaning from cardiopulmonary bypass after cardiac surgery in children with pulmonary hypertension and ventricular dysfunction are reported. Children fail to respond to conventional therapy combining nitrovasodilators and inotropic support and react successfully to combined inhaled nitric oxide (NO) and epinephrine or left atrial infused norepinephrine. Postoperative NO inhalation must be prolonged and no toxicity appears. Pulmonary endothelial function recovers only after several days.