The occurrence of concealed infection or "natural remission" in infective endocarditis was investigated microscopically in 35 consecutive patients (36 valves) with infective endocarditis (between April 1987 and May 1995). Four patients were considered as having concealed or silent infective endocarditis. Preoperative diagnosis of these patients was mitral valve prolapse, rheumatic aortic valve stenosis with insufficiency, aortic valve prolapse and hypertrophic cardiomyopathy, respectively. These patients did not present with any clinical signs of infective endocarditis such as cardiac murmur and ventricular dysfunction. Histological examination of the excised valves revealed valvular perforation, small round cell infiltration, neovascularization, remnants of vascular smooth muscle cells, and organizing vegetations. These findings are consistent with the histological findings of infective endocarditis. Latent infective endocarditis may be present without inflammatory manifestation.