http://www.nhlbi.nih.gov/health/dci/Diseases/hb/hb_whatis.html
National Heart, Lung, and Blood Institute, National Institutes of Health
This publication discusses heart block, which is a problem that occurs with the heart's electrical system. It occurs when the electrical signal is slowed or disrupted as it moves through the heart. The page links to additional information about heart block including types, causes, who is at risk, signs and symptoms, diagnosis, and treatments.