The occlusion of the left main coronary artery is rare and generally fatal. However, some subjects do survive. The two conditions necessary for survival appear to be the existence of a dominant right coronary artery and above all a rapidly functional left-right collaterality. The time lapse between occlusion and the introduction of an efficient collateral system is fundamental to patient survival. If the time lapse is too long, there is a risk of myocardial infarction, often complicated by cardiogenic shock, with a poor prognosis even after deocclusion. In this study, the case is reported of a patient with left main coronary artery occlusion presenting as unstable angor without an increase in enzymatic levels, and with a totally functional left-right collaterality. Deocclusion angioplasty was successfully performed. Finally, the short- and medium-term results of left main coronary artery angioplasty have been discussed.