Every day for 10 years, a seemingly heart-healthy 53-year-old woman experienced rapid and irregular heartbeats. She had no personal or family history of hypertension or hyperthyroidism. She did not suffer from myocardial or coronary artery disease, or any abnormalities of the heart as best doctors and medical science could determine. Yet, she complained of heart palpitations and dizziness nearly to the point of fainting.