good cardiac doctors near me A cardiac arrhythmia is an abnormal heart rhythm where the heart beats too fast (tachycardia, >100 bpm), too slow (bradycardia, <60 bpm), or irregularly. Caused by faulty electrical impulses or underlying heart conditions, symptoms include palpitations, dizziness, fainting, and chest pain. While some are harmless, others require medical treatment to prevent stroke or heart failure.