We report on a case of coronary sinus rupture that happened during placement of a cardioplegia balloon catheter and its subsequent repair. First, the defect was oversewn, however, not successfully. Under cardiopulmonary bypass and cardioplegic arrest, a pericardial patch was used to reconstruct the coronary sinus. Six months after the operation, blood drained during diastole into the right atrium but the flow was partially reversed during systole.