Disclosed herein is a method for predicting a patient response to a sodium ion channel blocker such as mexiletine when the patient has LQT syndrome or an arrhythmia. The method generally comprises determining a plurality of parameters associated with sodium ion channels; generating a model for patient response by using a partial least squared (PLS) regression analysis on said plurality of parameters; and using the model to predict the patient response if the patient is administered a sodium ion channel blocker such as mexiletine.