An intrapericardial teratoma associated with a large pleural effusion and elevated aortic outflow velocity was diagnosed at 23.6 weeks' gestation. Less than 4 weeks earlier, an obstetric scan, including a four-chamber heart view, had been normal In less than a week following diagnosis, fetal hydrops and bradycardia developed. 'Heroic' pericardiocentesis was declined by the patient, and the fetus died. This case demonstrates the potential for rapid growth in pericardial teratomas, and illustrates the possibility of anticipating fetal compromise from tumor mass effect, when intracardiac Doppler studies are abnormal. Implications for management of these rave tumors, and specifically for the hypothetical role of fetal surgery are discussed.