Sudden death is defined as a death that occurs suddenly, develops during an unpredictable course, and is due to natural or unnatural causes. Although there is no universally standardized definition on how "sudden" a sudden death is, WHO defines sudden death as a death that occurs within 24 hours after the onset of symptoms. The aim of this study is to present 2 rarely reported autopsy cases and to emphasize the importance of systemic autopsy at sudden death. On macroscopic examination, crescent-shaped, thick, fibrous membranes, located 5 mm and 3 mm away from the aortic valves, were detected. Fibrous membranes extended from the ventricular septum to the left ventricular outflow tract, thus apparently narrowing this region. Left ventricular wall and septum were slightly thickened, and there were scattered grayish-white areas of a small diameter. These became more intense in the septum and myocardium of the left ventricle on the anterior plane of the myocardial sections. In both cases, the aortic valves of were thickened and also markedly narrowed on one of them. In this case, the fibrous membrane adhered to the aortic valve and extended to the anterior leaflet of the mitral valve at one side. Both aortic valves comprised 3 leaflets. Other valves and coronary arteries showed no macroscopic pathologic findings. Microscopic examination of both cases demonstrated that the fibrous membrane comprising abundant collagen fibers was situated on the ventricular septum. Hypertrophy, moderate to severe interstitial fibrosis, and focal areas of scarring were observed in the specimens taken from the septal and ventricular myocardium. No abnormality was found on the conduction system examinations. Toxicologic analysis results in blood were negative. Based on the findings, membranous-type (discrete type) subvalvular aortic stenosis, diagnosed during the autopsy, was considered as the cause of sudden death in both cases.