A fetus presented with a large pericardial effusion caused by a right atrial transmural tumor. Correct prenatal diagnosis by use of targeted fetal echocardiography indicated that treatment was not required until the gestational age of 36 weeks. At that time, cesarean section was performed because early signs of imminent cardiac tamponade developed ("swinging heart"). At birth, the pericardial effusion was drained with a percutaneous drain. Elective surgical resection was performed on day 6 of life. Histologically, the tumor was a benign capillary hemangioma.