Abstract The cardiac involvement of hydatid cyst, which is rarely seen, with the location of asymptomatic huge cyst in the interventricular septum (IVS) is an extraordinary condition. We report an isolated cardiac hydatid cyst located in the IVS in an 18-year-old man diagnosed incidentally by transthoracic echocardiography. Cardiac magnetic resonance imaging confirmed a mass lesion of 47×74 mm in diameter located at the base of IVS. The cystic content and its germinative membrane were resected and the cavity was applicated under cardiopulmonary bypass. Postoperative course was uneventful and the patient was discharged on the 6th postoperative day, with oral albendazole therapy.