Hypersensitivity myocarditis presenting as atrioventricular block and wide complex tachycardia in a toddler.

A 13-month-old boy presented with acute onset of complete atrioventricular block and wide complex tachycardia but normal hemodynamics. Endomyocardial biopsy disclosed active myocarditis with eosinophils, suggesting a hypersensitivity reaction. With no treatment, the rhythm disturbance resolved within days of onset. Our patient's presentation and self-limited illness is unique. To our knowledge, this is only the second reported case of eosinophilic myocarditis in a young child or infant.