Epicardial cysts are rarer benign tumors than pericardial cysts. 17- year old boy presented with chest pain and palpitations and was diagnosed as mediastinal mass (pericardial cyst) on the basis of MRI and echocardiography. Surgical resection via thoracotomy was planned. Intraoperatively, the cyst was found to be epicardial in origin with close proximity to posterior descending artery. Therefore resection was concluded via midline approach and cardiopulmonary support. Despite detailed preoperative investigation and assessment, misdiagnosis of cardiac masses cannot be completely ruled out. Any undesired intraoperative diagnosis should be carefully dealt and a safer alternative approach can be considered for a better outcome.