The changes in 15 cases of viral myocarditis and 28 cases of dilated cardiomyopathy were reported and compared, which were the pathological changes of endomyocardial biopsy; NK cells activity; % of peripheral T lymphocytes and its subsets determined by using OKT3,4,8 (OKT3-peripheral total lymphocytes; OKT4-helper cells; OKT8-suppressive cells) monoclonal antibody; values of immunoglobulin IgG, IgA, IgM; titer of coxsackie B antibody neutralization test. And a discussion on their relationship was included.