Two surgical cases of mitral valve disease with severe pulmonary hypertension were reported, in which pulmonary hypertensive crisis (PHC) was a really serious problem to be treated. The first case (60-year-old woman) had atrial fibrillation and her pulmonary artery pressure was 68/32 mmHg (Pp/Ps = 0.63) and mean pulmonary wedge pressure was 26 mmHg with a high v wave (46 mmHg). PHC developed immediately after the cessation of artificial cardiopulmonary bypass, and intraaortic balloon pumping was performed. However, it was difficult to wean from the assist circulation, and then PGE1 and isoproterenol were given into the pulmonary artery and epinephrine and norepinephrine were given into the left atrium, and we succeeded in weaning from the assist circulation. The second case (58-year-old woman) had high pulmonary artery pressure (86/37 mmHg) and the Pp/Ps was 0.73. According to the experience of the first case, prevention of PHC started during cardiopulmonary bypass, giving PGE1, nitroglycerin and torazoline into the pulmonary artery. This led to the easy weaning from cardiopulmonary bypass. PHC may be seen even in cases of acquired valvular disease, and the prevention is mandatory for uneventful surgery.