A Dr. Douglas E. Severance, MD , Family Medicine, answered. Cardiologists usually treat atrial fibrillation, which is the most common type of abnormal heart rhythm, or arrhythmia. An electrophysiologist is a cardiologist who specializes in arrhythmias. However, other kinds of doctors can also treat atrial fibrillation, and who you see usually depends on the type of health care plan you have.