Sixty-eight patients of clinically diagnosed myocarditis, 0--15 years of age, were followed up and analyzed. Forty (58.8%) were males. The majority were older than 5 years. Clinical courses were rather mild, chronic and self-limiting at large. Only 1 case had a relation to chronic cariomyopathy. Exertional symptoms (chest pain, chest distress, syncope) were seen in 25 (36.8%). ECG changes were very common: the majority were nonspecific ST elevation, depression or both, mainly in leads II, III, V5 and V6. Positive Master' test, prolonged QTc, widened mean spatial QRS-T angle and various arrhythmias were also observed. Cardiac performance, estimated by echocardiogram and phono-mechanocardiogram was lowered in 41 (60.3%). Large IV sound and large A wave in apexcardiogram were also frequently found. All but 3 patients showed continuous elevation of serum enzymes, namely, LDH, LDH-1/LDH-2, CPK, CPK-MB, HBD and GOT. Etiological evidences were obtained by serological study in 11 cases (16.2%): 2 of Coxsackie B-1, 3 of Coxsackie B-2, 1 of Coxsackie B-4, 2 of mycoplasma pneumoniae, 1 of cytomegalovirus, 1 of ECHO-7 and 1 of rubella. We proposed a criteria for diagnosis of myocarditis as follows: (1) Exertional symptoms. (2) ECG findings. (3) Serum enzyme abnormality. (4) Lowered cardiac performance. (5) Cardiomegaly. (6) Changing character of all signs and symptoms.