The morphologic features of alcoholic cardiomyopathy in human sudden death compared with those of experimental alcoholic cardiomyopathy (6 weeks of alcohol administration and simultaneous inhibition of catalase activity) proved to be nearly identical. Regular and similar alterations in alcoholic cardiomyopathy in both human victims of sudden death and experimental rats are described as a complex of alterations characteristic of alcoholic cardiomyopathy. This complex of changes was used as the basis for morphologic diagnosis of endomyocardial biopsy in two groups of patients: I) chronic alcoholics (second to third stages), and II) patients with clinically diagnosed congestive cardiomyopathy. Typical signs of alcoholic cardiomyopathy were found in 9 of the 11 patients in the first group and in 6 of 18 in the second group. The fact that the features of alcoholic cardiomyopathy were not found in all cases of chronic alcoholism supports the hypothesis that the administration of alcohol itself is not sufficient for the development of this disease. The level of enzyme activity in the metabolism of alcohol appears to be of great importance. This hypothesis is confirmed by experiments with rats in which this disease developed only when there was simultaneous alcohol administration and inhibition of catalase activity. Histochemical study showed that the alterations of enzyme (both energetic and alcohol metabolism) in rats were similar to those found in the biopsy specimens from patients with alcoholic cardiomyopathy. Certain questions regarding the pathogenesis of alcoholic cardiomyopathy are discussed.