BackgroundThere is a high incidence of ventricular arrhythmia and sudden death in patients with heart failure. Unfortunately, currently available antiarrhythmic agents have only limited efficacy and may result in proarrhythmia and hemodynamic deterioration in these patients. Methods and Results We studied the acute effect of intravenousMethods and ResultsWe studied the acute effect of intravenous magnesium chloride on the frequency and severity of ventricular arrhythmia in 30 patients with symptomatic heart failure using a double-blind, placebo-controlled crossover design. The left ventricular ejection fraction was 23.0±8.0% (mean±SD). No patient had a history of symptomatic ventricular arrhythmia or was receiving antiarrhythmic agents, calcium channel antagonists, or P-blockers. Patients were randomized to receive placebo (5% dextrose [D5W] in water alone) or magnesium chloride in D5W given as a bolus of 0.3 mEq/kg over 10 minutes followed by a maintenance infusion of 0.08 mEq/kg per hour for 24 hours. The magnesium concentrations 30 minutes and 24 hours after the bolus were 3.6±0.1 and 4.2±0.1 mg/dL, respectively. There was no significant change in serum potassium concentration during magnesium administration. Blinded analysis revealed that administration of intravenous magnesium chloride, compared with placebo, significantly decreased total ventricular ectopy per hour (mean±SEM, 70±26 versus 149±64.P< .001), couplets per day (23±11 versus 94±59,P= .007), and episodes of ventricular tachycardia per day (0.8±0.2 versus 2.6±1.0,P= .051).ConclusionsIntravenous magnesium chloride administration reduces the frequency of ventricular arrhythmia in patients with symptomatic heart failure.