To examine factors affecting heart rate variability (HRV) and the role of HRV in heart disease. Specifically, to examine the role of HRV: as a predictor of fatal and nonfatal ischemic heart disease over a six year follow-up of the Atherosclerosis Risk in Communities (ARIC) population based, bi-ethnic cohort; on the six year progression of carotid atherosclerosis measured by B-mode ultrasound; and on the incidence of hypertension. Also, to study the effect of elevated fasting insulin, glucose, diabetes mellitus, and other metabolic abnormalities on changes in HRV over nine years of follow-up.