Non-involuting congenital haemangioma (NICH) is a rare cutaneous vascular tumour about which little is known. Fully formed at birth, NICH enlarges proportionally with age but fails to involute as most infantile haemangiomas do. In addition to this unique clinical character, NICH demonstrates several distinct features. Doppler and magnetic resonance imaging (MRI) studies reveal persistent high-flow arterial feeders and a tumour-like capillary blush; however, NICH fails to demonstrate early venous opacification in contrast to arteriovenous malformation (AVM). NICH lesions also contain microscopic dermal arteriovenous fistulas as well as prominent interlobular veins. Here, we present the first known case of NICH-related high-output cardiomyopathy in a 2-year-old boy.