The case of a 12 year old schoolgirl with heart failure due to varicella myocarditis is reported. Heart failure and cardiogenic shock were evident 21 days after the appearance of the rash, and cardiac transplantation was performed two weeks later. Myocarditis is a serious complication of varicella zoster infection and heart failure may be fulminant. Endomyocardial biopsy changes consistent with myocarditis were documented six days after the start of heart failure. The histological changes, however, developed into those of idiopathic dilated cardiomyopathy (with anisonucleosis and fibre width variation) over a seven day period. This case provides further evidence for the link between viral myocarditis and idiopathic cardiomyopathy and underlines the value of immediate endomyocardial biopsy in heart failure of recent onset. Cardiac transplantation led to a rapid and full recovery.