Two 38 and 53-year old male patients with unstable angina, whose hemodynamic study showed an isolated stenosis of the left coronary artery ostium, were submitted to a surgical angioplasty of the left main coronary artery (LMCA) with saphenous vein patch. At the end of the operation, the patients presented intermitent myocardial isquemia. One of them led to abrupt cardiogenic shock which reversed completely. The postoperative hemodynamic study demonstrated excellent left main coronary artery patency and normal left ventricular of LMCA has been proposed as an alternative technique to the treatment of ostial lesions, the surgical team should be prepared to face severe operative morbidity. The LMCA spasm has been considered as a possible etiology of that event.