Magnesium to Reduce Implantable Cardioverter Defibrillator (ICD) Shocks and Improve Patient's Quality of Life.

Not all ICD shocks are for ventricular arrhythmias. Some patients receive shocks when they
have arrhythmias in the atria (top chambers of the heart). These are called inapproriate
shocks, but the pain is similar to the pain patients feel with an appropriate shock (a shock
for a ventricular arrhythmia). This study is being conducted to determine if taking
magnesium can reduce the number of shocks patients with ICDs experience and to see if
magnesium supplementation improves patients quality of life. Magnesium's impact of the
electrocardiogram (ECG) and intracellular magnesium concentrations will also be studied.

Comparison: Magnesium compared to placebo in patients with ICDs to evaluate the number of
ICD shocks and patient perceived quality of life.

Inclusion Criteria:newly implanted ICD or recent ICD shock (within 6 months) -

Exclusion Criteria:inability to swallow, a non-cardiac disease with a survival prognosis
of less than 12 months, hypermagnesemia, a creatinine clearance less than 30mL/min, lactic
acidosis or systemic acidosis syndrome, or previous intolerance to magnesium L-lactate.