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We report the case of a 71-year-old-man, a smoker, admitted for unstable angina. Subsequent investigation revealed complete proximal occlusion of the left main coronary with an unusual collateral circulation. The left coronary artery was filled by a large conus branch originating from the right sinus of Valsalva. This case shows the importance of looking for atypical collateral circulation in patients with chronic occlusion of the left main coronary artery and normal left ventricular function.