The study has been extended through November 2005 to continue examination of the investigator's Twin CV Health cohort (519 pairs of twins who will be 14 to 25 years old). The study provides the unique opportunity to better understand the effects of sodium ion (Na+) retention as a mechanism augmenting systemic vascular resistance responsivity (SVR) and changes in vascular function (i.e., endothelium dependent arterial dilation; EDAD), ventricular structure (i.e., left ventricular mass; LVM) and 24-hour ambulatory BP (ABP). The specific aims are to determine: 1) To what extent is environmental stress related to stress induced Na+ retention, SVR responsivity and preclinical markers of essential hypertension risk and are these relationships stronger in African Americans than Caucasian Americans; 2) Whether stress induced Na+ retention is a pathway linking environmental stress with preclinical markers of essential hypertension risk; and 3) Whether behavioral factors (i.e. John Henryism, anger expression, social support, physical activity) moderate effects of environmental stress on stress induced Na+ retention and/or SVR responsivity and in the preclinical markers of essential hypertension risk, particularly in African Americans.