We examined the cardiac conduction system of three alcohol abusers who died suddenly. Cases 1 and 2 showed mitral valve disorder (mitral valve prolapse and rheumatic valvular disease), while Case 3 showed mild Ebstein's anomaly. On examination of the conduction system, Cases 1 and 2 showed severe fibrofatty infiltration into the conduction system, and we conclude that these findings were probably a complication of alcohol abuse. Both cases also demonstrated severe small artery disease. The conduction system of Case 3 showed an anomalous location of the bundle of His with its fragmentation. These three cases suggest that such considerable conduction system abnormalities may be significant findings in alcohol abusers with valvular disease. We consider that alcohol intake may be one of the direct accelerating factors for arrhythmogenic potential to the abnormal conduction system in alcohol abusers who have asymptomatic valvular disease.