In this study, we are prospectively testing whether polymorphisms in ion channels and ion channel modifying genes are associated with arrhythmias in a population with internal cardioverter-defibrillators (ICDs) and poor LV function. We will test the hypothesis that functional polymorphisms in the coding sequences and promoter regions of cardiac genes (e.g. ion channels, beta-adrenergic receptors) predispose individuals to arrhythmias and /or heart failure progression.