Two-dimensional echocardiography has become the diagnostic method of choice for identifying intracardiac masses. However, adjacent extracardiac structures may closely mimic intracardiac masses on the two-dimensional echocardiogram. Five cases of a previously unrecognized phenomenon in which a diaphragmatic hernia mimicked an intraatrial mass are reported. Techniques to identify a diaphragmatic hernia properly on two-dimensional echocardiographic examination and distinguish it from intracardiac masses are discussed.