Aneurysms that develop at sites of cardiac ventriculotomy incisions are recognized but infrequent consequences of such procedures. Their development appears to be dependent on 2 major factors: 1) the peak systolic pressure within the ventricle after the incision, and 2) the length of the incision. The incidence of postventriculotomy aneurysm is far greater in the left ventricle than in the right because of the differences in peak pressures in each chamber. Herein, we describe a patient with both subvalvular pulmonic stenosis and peripheral pulmonary arterial stenoses in whom a massive right ventricular (RV) outflow tract aneurysm developed after operative relief of the subvalvular obstruction. A 30-year-old woman had a precordial murmur at birth and cyanosis and clubbing of the digits by age 7 years. Results of 4 cardiac catheterization studies confirmed the presence of subpulmonic obstruction, peripheral pulmonary arterial stenoses, and a right-to-left shunt through a patent foramen ovale. Syncope occurred at age 12 years, and by age 15 had become frequent and severe. The subpulmonic stenosis was operatively relieved at age 15 years by excision of portions of crista supraventricularis myocardium. A Teflon fabric patch was used to enlarge the RV outflow tract. The patent foramen ovale was sutured closed. At necropsy, the heart with the aneurysm weighed 830 g. The RV outlfow incisional aneurysm was partially filled with laminated thrombus and lined by focally calcified fibrous tissue. The aneurysm partially compressed the pulmonary trunk, left atrium, and left anterior descending coronary artery.