The major features of myocarditis are disturbances in heart rhythms, congestive heart failure, or cardiogenic shock. ECG changes include nonspecific ST-Twave changes, while two-dimensional echocar-diograms reveal (1) normal ventricular size but decreased contractility early in the dis-ease and (2) later heart enlargement with thinning of the muscle in chronic cases. In addition, both ventricles may be affected in chronic cases. None of the clinical fea-tures described are diagnostic for myocar-ditis, and until the use of the endomyocar-dial biotome, the diagnosis could only be established with certainty by postmortem examination.
The incidence of the disease varies from 1 to 10/100,000. The reasons for this wide discrepancy may be related to exposure to the different types and strains of cardiotro-pic viruses as well as genetic differences in host populations. Many patients recover spontaneously inter supportive treatment but the five-year survival of biopsy-proven giant cell myocarditis is only 56 percent, and in pediatric patients, the mortality rates may be even higher.