A case of pericardial cyst with partial erosion into the anterior wall of the right ventricle is presented. Cardiopulmonary bypass was necessary for excision of the cyst. This report helps to alert surgeons of the possible need for cardiopulmonary bypass during the removal of some pericardial cysts, especially in patients with signs and symptoms of infection and in whom preoperative imaging fails to show distinct margins between the cyst and cardiac structures.