The aim of this study to evaluate the prevalence and prognostic signicance of T-wave alternans in patients with severe CHF. We hypothesize that: (1) patients with T-wave alternans (regardless of the etiology of their heart failure) will have an increased cardiac mortality compared with patients who do not have T-wave alternans, and (2) T-wave alternans will be significantly more common in patients with severe CHF from an ischemic cardiomyopathy than in patients with severe CHF from a non-ischemic cardiomyopathy.