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Ventricular tachycardia is an arrhythmia, or irregular, rapid heart rhythm characterized by a series of at least three beats, arising usually from a single site within the ventricle, at a rate in excess of 100 beats per minute. Ventricular fibrillation is the term for the very rapid and irregular contractions of the ventricle that prevent the effective pumping function of the heart muscle, which if prolonged can lead to death. The effectiveness of the antiarrhythmic drug amiodarone was examined in 97 patients with ventricular tachycardias and 48 patients who had survived ventricular fibrillation. The patients had tried an average of four different drug treatments before starting amiodarone. The initial dose of amiodarone was 845 milligrams for the first two weeks, which was combined with another antiarrhythmic agent in half of the patients. After two weeks, the patients were given 410 milligrams of amiodarone daily and followed-up for three years, or until death or withdrawal from therapy. The average duration of treatment with amiodarone was about 39 months. The incidence of death due to an arrhythmia was about five percent in the first year and three percent in the second and third years of follow-up. Thirty-six patients died during the study. Survival was associated with the function of the left ventricle. Seventeen percent of patients were withdrawn from the study because of toxic side effects, six percent because of toxic effects on the lung. Amiodarone appears to be effective in treating arrhythmias in patients who do not respond to treatment with other antiarrhythmic agents. (Consumer Summary produced by Reliance Medical Information, Inc.)