Atrial fibrillation is a common cardiac arrhythmia that needs development of more effective medications. Propafenone is a medicine currently used to treat atrial fibrillation and is a mixture of two compounds, (R)-propafenone and (S)-propafenone. The investigators have discovered that purified (R)-propafenone may be more effective than (S)-propafenone for treatment of atrial fibrillation, and that (S)-propafenone reduces the efficacy of (R)-propafenone when administered as a mixture. This study will compare the ability of (R)-propafenone, (S)-propafenone, and placebo to suppress the induction of atrial fibrillation in participants undergoing an atrial fibrillation ablation procedure.