Current drug therapies to suppress AF are incompletely and unpredictably effective and carry significant (albeit generally small) risks of serious adverse effects, including drug-induced long QT syndrome (diLQTS), other forms of proarrhythmia, increased mortality through uncertain mechanisms, and extracardiac toxicity. Identification of clinical and genetic subtypes of AF will permit stratification of therapeutic approaches and thereby facilitate the practice of personalized medicine. Furthermore, limited success of drug therapy and increase in drug toxicity in AF is probably because the arrhythmia represents a final common pathway of multiple initiating mechanisms, including those some that are genetically-defined.