In the spring and summer of 2008 two seriously ill male infants were admitted to a paediatric intensive care unit. Initially, both had a fever, were drinking less and were pale complexioned. Physical examination revealed tachycardia, slow capillary filling and liver enlargement. Within a few hours, both infants developed circulatory and respiratory failure. A chest radiograph showed that the heart was enlarged and echocardiography revealed that the pump function of both ventricles was severely diminished. Myocarditis caused by Coxsackie virus B3 was diagnosed when the virus was demonstrated in serum and faeces. At the last follow-up, one infant still had severe pump function disorders, and the other one died. Coxsackie virus B3 is a non-polio enterovirus that usually causes mild clinical syndromes but is also associated with myocarditis and overwhelming, systemic neonatal infections. In neonates with mild symptoms one should be alert to progression to circulatory insufficiency, especially if the mother experiences a flu-like illness in the perinatal period. Early recognition of heart failure and adequate diagnostic testing for cardiotropic viruses is important as morbidity and mortality is considerable.