Some people with atrial fibrillation may be prescribed blood thinners to reduce the risk of blood clots. Others may be treated with medications that work against arrhythmia, such as sodium channel blockers and potassium channel blockers. A procedure called ablation eliminates the heart tissue believed responsible for the disruptive activity. That can be done with heat or cold. Recently, Stanford became one of the first hospitals to offer new ablation treatment called Focal Impulse and Rotor Modulation (FIRM). With FIRM, ablation is guided by a new electrical activity mapping software that pinpoints in the heart the exact electrical sources that drive atrial fibrillation. These sources, called rotors because of their circular shape and spinning motion, are small electrical sources that cause the disorganized activity that produces atrial fibrillation. In humans, the existence of these rotors had been suspected but only recently confirmed. One of Stanford’s leading experts in atrial fibrillation, Sanjiv Narayan, MD, PhD, discovered these rotors through research and helped develop the mapping software. In 2013, the FDA approved the mapping catheter used in FIRM ablation. In a study first presented in 2011, the multicenter CONFIRM clinical trial of 107 patients showed that two years after treatment, 86% of those treated with FIRM ablation had not had a recurrence of atrial fibrillation, compared to 44.9% of those who received traditional therapy. FIRM ablation can be completed in less time than traditional ablation, and is being used at Stanford for routine clinical care and as part of several clinical trials with or without conventional ablation (pulmonary vein isolation).