A surgical case of diverticulum in the left ventricular apex is presented. A two-dimensional echocardiogram and magnetic resonance image showed a calcified tumor buried in the marked hypertrophied apex of the left ventricle. Enucleation of the oval and hard tumor (4 x 2.5 x 2.5 cm) was performed through the apex, and the defect was anastomosed by buttress sutures. Histologic examination demonstrated that the tumor cavity was filled with a thrombus encapsulated by thickened and calcified endocardium that extended to the left ventricular cavity. In this report, the etiology of the diverticulum with a hypertrophied myocardium is discussed.