Mortality statistics from multicenter studies outlined some high risk characteristics of patients with coronary heart disease subjected to coronary angiography. Among these, the left main disease carries the worst prognosis. The features of left main disease patients with a higher mortality probability during coronary angiography are described. Data were collected prospectively on 4844 patients subjected to coronary angiography. No death was recorded in patients without left main disease (4641 patients) independently of other risk factors: number of diseased vessels, NYHA status, clinical picture, or ejection fraction. From the 203 patients with left main disease, 30 had a left ostial lesion (14% of the patients with left main disease). The three patients who died during the procedure were among those with left ostial lesion. Therefore, despite the fact that the incidence of mortality in all patients in general who are subjected to coronary angiography was small (0.06%) there was a subgroup of patients with ostial lesion who carried high mortality (10%) (p<0.0009).