Atrioventricular block in the young is a rare condition. It is defined as congenital when diagnosed in utero, at birth or during the first month of life. Childhood atrioventricular block is defined when diagnosis occurs after the first month of life and until the age of 18. It can be isolated (when occurring in a structurally normal heart) or associated with a congenital or acquired cardiac disease or other primary causes. The definitive treatment of congenital or childhood high-degree atrioventricular block consists in pacemaker implantation for high risk or symptomatic patients. In this article we report a case of probably idiopathic isolated childhood high degree atrioventricular block presenting with a longstanding history of effort intolerance, successfully treated with implantation of a double chamber pacemaker.