2. Significant cardiovascular abnormalities including any one of the following: Congestive heart failure, Clinically significant hypotension, Symptoms of coronary artery disease, Presence of cardiac arrhythmias on EKG requiring drug therapy; or Patients with a history of cardiovascular disease. (Patients with the above will undergo a cardiac evaluation which can include a stress test and/or echocardiography. Results of this evaluation will be considered before excluding patients on the basis of cardiovascular abnormalities). Subjects with evidence of stress-induced cardiac ischemia or ejection fraction less than 55% will be excluded.