Although echinococcosis (echinococcal hydatidosis) is common in sheep-raising countries such as Turkey, cardiac involvement is rare; the presence of a hydatid cyst in the interventricular septum is rarer still. We report a case of hydatid cyst of the interventricular septum that was first revealed by 2-dimensional echocardiography and then confirmed by right ventricular angiography. The cyst was removed surgically under cardiopulmonary bypass. Within the context of the medical literature concerning this rare lesion, we discuss this case and 10 other cases of cardiac hydatidosis, previously unreported in the world literature, that we have treated from January 1967 through January 1987.