• A slow heart rate, usually below 60 beats per minute.
  Harvard Dictionary of Health Terms
  Harvard Medical Publishing, 2011
• A slower than normal heart rate (in adults, slower than 60 beats per minute).
  Human Phenotype Ontology (HPO)
  The Human Phenotype Ontology Project, 2025
• An abnormally low heart rate for age.
  NICHD Pediatric Terminology
  U.S. National Cancer Institute, 2021
• An abnormally slow heart rate. Thresholds for different age, gender, and patient populations exist.
  NCI
  U.S. National Cancer Institute, 2021
• Cardiac arrhythmias that are characterized by excessively slow HEART RATE, usually below 50 beats per minute in human adults. They can be classified broadly into SINOATRIAL NODE dysfunction and ATRIOVENTRICULAR BLOCK.
  NLM Medical Subject Headings
  U.S. National Library of Medicine, 2025
• Excessive slowness in the action of the heart, usually with a heart rate below 60 beats per minute.
  CRISP Thesaurus
  National Institutes of Health, 2006
• Bradycardia is a slower than normal heart rate. The hearts of adults at rest usually beat between 60 and 100 times a minute. If you have bradycardia (brad-e-KAHR-dee-uh), your heart beats fewer than 60 times a minute.
  Mayo Clinic
  Mayo Foundation for Medical Education and Research, 2025
• While some consider bradycardia to be a heart rate <60 bpm, this is in dispute and most consider rates of <50 bpm to represent bradycardia. A study of 500 normal people, using ECG recordings, showed the mean afternoon heart rate to be 70 bpm in men and women, with two standard deviations being 46 to 93 bpm in men and 51 to 95 bpm in...
  Epocrates
  Athenahealth, Inc., 2019
• Bradycardia, type of arrhythmia (abnormal heart rhythm) characterized by slowing of the heart rate to 60 beats per minute or less. A slow heart rate in itself may have little medical significance; bradycardia is frequent among young adults, especially in highly trained athletes or during sleep....
  Encyclopedia Britannica
  Encyclopedia Britannica, Inc., 2025