Objective To understand the shift of apoptosis in lymphocyte of children with myocarditis, to investigate the pathogenesis of myocarditis.Methods To detect the shift of apoptosis in T-lymphocyte by immunofluorescence among 41 children with myocarditis including infection of virus and mycoplasma, and the alteration of T-lymphocytic subgroup and immunoglobulin at the same time. Results The apoptosis of lymphocytes in myocarditis group was higher than that of normal group, and T-lymphocytic subgroup CD 4 +, CD 4 +/CD 8 + were distinctly descented, CD 8 + was elevated(P<0.01). Conclusions The excessive apoptosis of lymphocytes lead imbalance of the amount. The low functions of T-lymphocyte and humour immunity are one of the important cause of the myocarditis induced by the infection of virus or mycoplasma.