Acute myocarditis associated with transient marked myocardial thickening and complete atrioventricular block

A 17-day-old male infant with acute myocarditis developed complete heart block and cardiogenic shock. In addition, extensive concentric thickening of the left ventricular walls and diminution of the ventricular cavity were demonstrated by serial echocardiography. The echocardiographic findings mimicked a nonobstructive hypertrophic cardiomyopathy. However, the wall thickness gradually returned to normal, coincident with clinical improvement. This unusual myocardial thickening may have resulted from myocardial edema or cellular infiltration. Its relationship to high-dose steroid therapy is unclear.