A four year old child was admitted for investigation of a cardiac murmur and cardiomegaly. Echocardiography showed a large left ventricular tumour, the extension of which was accurately defined by nuclear magnetic resonance imaging and the etiology confirmed by coronary angiography. Holter recordings showed salvoes of ventricular tachycardia. This is an interesting case because, despite echocardiography and nuclear magnetic resonance imaging, the precise nature of the tumour was revealed only by coronary angiography. This investigation also showed a significant decrease of the left ventricular ejection fraction. It is the only described haemangioma complicated by this type of ventricular hyperexcitability. Therefore, coronary angiography would seem to be necessary in the investigation of isolated myocardial masses which remain unidentified by non-invasive methods.