Prescribing cardiac drugs in children differs in a number of ways from adult practice. In general terms cardiac drugs used in children are used by extension from adult practice without most of the drugs being tested in children (‘off label’). In addition, the aetiology of heart disease in children differs from adults. For example, heart failure in children is due to idiopathic muscle disease but heart failure in adults is more often secondary to hypertension or due to ischaemic heart disease. Moreover, the prescription of cardiac drugs for a child will often be initiated by a specialist cardiologist rather than a generalist.