Prospective Observational Study of the ICD in Sudden Cardiac Death Prevention

This study is observing people who have a heart device called an ICD (implantable cardioverter-defibrillator) — a small device in the chest that delivers electric shocks to prevent sudden cardiac death — to learn how well it works over time. **You may be eligible if...** - You have had a heart attack at least 4 weeks ago, or have had weak heart muscle for at least 9 months due to a non-heart-attack cause - Your heart pumps at 35% or less of its normal capacity (low ejection fraction) - You recently had your ICD battery replaced (within the last 24 months) as a preventive measure against sudden cardiac death - Your ICD was implanted to prevent a first cardiac arrest (primary prevention) **You may NOT be eligible if...** - Your ICD was implanted after you already survived a cardiac arrest (secondary prevention) - You are unable or unwilling to give consent - You have severe heart failure (New York Heart Association Class IV — unable to do any activity without discomfort) - You already needed a pacemaker for rhythm problems before getting the ICD Talk to your doctor to see if this trial is right for you.