The study examines the relationship between PTSD and cardiac function in a population-based sample of American Indians. The technical aims of this study involve: 1) the identification of American Indian men and women ages 18-52 who have a lifetime history of PTSD and are free from overt CVD; 2) the selection of an age-, sex-, and tribe-matched comparison group of American Indians who have no history of PTSD and are free from known CVD; 3) a comprehensive lifestyle and clinical evaluation of the PTSD and non-PTSD groups to assess CVD risk factors such as smoking, exercise, obesity, blood pressure, concentrations of blood lipids, and inflammatory and thrombogenic factors; and 4) a set of non-invasive tests of subclinical CVD and other measures of CVD risk. These tests include positron emission tomography (PET) myocardial perfusion imaging to examine coronary flow reserve, high-resolution ultrasound of the carotid arteries to measure carotid intima-media thickness, high-resolution ultrasound of the brachial artery to determine flow-mediated vasodilation, and ambulatory electrocardiographic monitoring, to assess heart rate variability (HRV). With these data, the study addresses the specific aims, which are: 1) to determine whether individuals with PTSD, compared with those without PTSD, show greater evidence of subclinical CVD, including a lower coronary flow reserve, increased carotid intimamedia thickness, and reduced forearm flow-mediated vasodilation; 2) to ascertain whether HRV is lower in individuals with PTSD compared to those without PTSD; and 3) to investigate the role of lifestyle (e.g., smoking, alcohol use, exercise, obesity), cultural (e.g., acculturation, religiosity), and biological (e.g., blood pressure, blood lipid and glucose concentrations) mediators in the relationship of PTSD with coronary flow reserve and HRV.