Provided is a method of facilitating the determination of treatment of a subject displaying atrial fibrillation, the method comprising determining a level of pitx2c expression in a sample from the subject and selecting a treatment based upon the level of pitx2c expression. Treatment with a sodium channel blocker may be selected if the level of pitx2c expression is determined to be reduced or below a predetermined threshold. Also provided are an assay system and a kit for use in the methods of the invention.
