Congenital right ventricular aneurysms and diverticula are rare congenital anomalies and prenatal detection is uncommon. Distinguishing between these two anomalies by imaging alone is difficult. Recently, we were asked to review a 21-week ultrasound that detected an "extra cardiac chamber." This represents the first report of an isolated out-pouching of the right ventricular free wall to be detected by prenatal screening ultrasound. Based on preoperative imaging, this out-pouching was diagnosed as a ventricular aneurysm, but intraoperative findings suggested it was a diverticulum. This case will review the differences between ventricular aneurysms and diverticula and illustrate the use and limitations of various imaging modalities used in their evaluation, both prenatally and postnatally. A plan of management is suggested.