Baseline visit procedures: The baseline visit will take place at the Vanderbilt Clinical Research Center (CRC). Patients will present to the CRC and be met by a study physician, who will perform a history and physical exam. The CRC nurse will draw 30 ml of blood for DNA extraction and subsequent genotyping. Plasma will be stored at -70 degrees C for future studies. Blood will be sent to the Vanderbilt inpatient laboratory for analysis of the basic metabolic panel. A baseline 12-lead ECG will be obtained for all patients and interpreted at the bedside by the study physician. For patients randomized to start sotalol first, a peripheral intravenous catheter will be placed. Once inclusion and exclusion criteria are confirmed, the patient will receive his/her first dose of study medication (sotalol 120 mg by mouth or flecainide 50 mg by mouth), which will be dispensed by the IDS and given to the patient. Per routine clinical practice, patients initiating flecainide will also be started on atenolol (25 mg by mouth daily) or diltiazem (120 mg long-acting by mouth daily) if the patient has contraindications to β-blockers to prevent the development of 1:1 conducted atrial flutter.