Glossary of terms related to heart rhythm disorders. Includes Atrial fibrillation (A Fib), Ejection fraction, Electrophysiology (EP) test, ACE inhibitors, Beta-blockers, Bradycardia, Tachycardia, Dyspnea, ICDs, pacemakers and more. From UpBeat.org, the Heart Rhythm Society’s Patient Resource Center. The Heart Rhythm Society represents physicians and scientists in the field of cardiac arrhythmia. Directory of cardiology subspecialists called electrophysiologists can be found under Find a Specialist.