Y-grafting is a common coronary grafting technique for performing composite coronary grafts. The outcome and efficacy of this technique have not been studied in detail in the literature. We report a case of an occlusion in the proximal limb of a Y-graft, changing it into a C-shaped conduit and causing a steal syndrome. Our aim is to raise the level of caution when performing this type of composite graft and to suggest how this complication can be managed postoperatively.