- Persons will be excluded if they have evidence of heart disease by history (Prior heart attack or bypass surgery, heart failure, or significant valvular disease) or abnormal resting electrocardiogram (EKG) consistent with prior infarct or latent ischemia (unless cardiovascular stress imaging or catheterization shows they do not have coronary artery disease). We will also exclude subjects with left or right bundle branch block on resting EKG (precludes recognition of ischemic EKG changes with exercise) or abnormal exercise EKG (> 1 mm ST segment depression 80 msec out in the ST segment for 3 consecutive beats).