Hypertrophic cardiomyopathy and primary endocardial fibroelastosis are rare pathologic lesions of the heart. We report a case of a male infant who died due to cyanotic heart failure after living 3 days. The autopsy findings showed that the patient had both obstructive hypertrophic cardiomyopathy and primary endocardial fibroelastosis. To our knowledge this case is unique in the literature of the last 15 years. The case was the first child of the family, whose history had no significance except the hypertensive treatment the mother had during pregnancy. In the autopsy it was observed that the left ventricle wall was diffusely involved and the ventricle cavity was extensively narrowed due to hypertrophic cardiomyopathy. In addition to significant stenosis in the aortic and mitral valves, and fibroelastosis in the endocard of the left ventricle, there were also lung edema, congestion in the liver, microvesicular fatty change in the hepatocytes, findings of loxia and circulatory disturbances. In the cytometric investigations, no considerable difference was observed between each of the ventricle myocards and the normal control myocard in terms of average Ag-NOR count, DNA ploidy and S-phase fractions.