Double drainage sites from a common venous confluence of the pulmonary veins of a mixed total anomalous pulmonary venous connection is a rare condition that is called a “double connection.” There have been very few reports of reoperation for minor drainage of a double connection. A 28-year-old male with double connection type (Ia: major drainage + IIa: minor drainage) mixed total anomalous pulmonary venous connection (TAPVC) was referred to our institution. He had undergone TAPVC type Ia (major drainage) repair at the age of 1 year. Postoperative enhanced computed tomography showed residual TAPVC IIa (minor drainage) at the age of 15 years. Therefore, the definitive diagnosis was double connection-type mixed TAPVC. Residual shunt gradually increased, and cardiac catheterization revealed an increased pulmonary blood flow/systemic blood flow ratio. Echocardiography showed enlarged shunt vessel and mild tricuspid regurgitation. Catheter intervention was considered too risky and, therefore, we performed patch closure of the residual shunt through a right atriotomy. The postoperative course was uneventful, and follow-up computed tomography showed shrinkage of the shunt vessel without any thromboembolic events.