Below are some helpful Internet resources on this topic. Mayo Clinic does not own or control any of these sites and is not responsible for their content. Inclusion of these sites does not imply endorsement by Mayo Clinic.
www.nhlbi.nih.gov
National Heart, Lung and Blood Institute
www.nlm.nih.gov
MedlinePlus — A service of the U.S. Library of Medicine and the National Institutes of Health