- History of myocardial infarction =< 6 months or congestive heart failure (CHF) requiring use of ongoing maintenance therapy for life-threatening ventricular arrhythmias; patients must have a New York Heart Association (NYHA) of class II or less; (NYHA class I: patients with no limitation of activities; they suffer no symptoms from ordinary activities; class II: patients with slight, mild limitation of activity; they are comfortable with rest or with mild exertion; class III: patients with marked limitation of activity; they are comfortable only at rest; class IV: patients who should be at complete rest, confined to bed or chair; any physical activity brings on discomfort and symptoms occur at rest)