The clinical and postmortem findings in a case of unexplained ventricular hypertrophy which simulated aortic stenosis is reported. Left ventricular puncture revealed a systolic pressure gradient of 130 mm. Hg between the left ventricle and aorta. At postmortem examination marked myocardial hypertrophy without chamber dilatation and a normal aortic valve were found. Reduction of the cavities of both ventricles by hypertrophied myocardium was striking, and may have been responsible for the finding of a pressure gradient at catheterization of the left side of the heart. The patient's brother, who has similar clinical and catheterization findings, may represent another example of this curious type of ventricular hypertrophy.