The purpose of this study is to determine whether waveforms of the intracardiac electrograms, acquired through an ICD, can be used:

• to predict malignant ventricular arrhythmias, requiring appropriate ICD therapies, and
• to predict progression of heart failure in patients with ICD.

Inclusion Criteria:

• history of acute MI at least 4 weeks old
• non-ischemic LV dysfunction for at least 9 months
• who have an EF < or = to 35%
• who was resuscitated from sudden cardiac arrest (ventricular tachyarrhythmia)
• undergone implantation of an FDA-approved ICD for primary or secondary prevention of SCD

Exclusion Criteria:

• inability or unwillingness to provide valid informed consent
• pregnancy
• any condition other than cardiac disease that was associated with a high likelihood of death during 1 year after enrollment

Patients with ischemic or non-ischemic cardiomyopathy undergoing ICD implantation for primary or secondary prevention of sudden cardiac death