The study has both a nested case-control design and a nested cohort design within the Strong Heart Study (SHS), an ongoing cohort study of 4,549 American Indians. The study utilizes previously collected specimens, baseline data, and the ultrasound measurement of carotid wall thickness (IMT) in SHS participants. Within the initial SHS cohort, 400 definite cases of incident myocardial infarction, coronary heart disease, and stroke are compared with 400 control individuals with no such diagnoses and matched for age, gender, and residence. Their prior serum specimens are analyzed for Chlamydia pneumoniae-specific IgG, IgM antibody, for cytomegalovirus-specific IgG antibody, and for C-reactive protein (CRP). In addition, assays are performed for antibodies to Helicobacter pylori, hepatitis A virus, (HAV) and herpes simplex virus (HSV) type 1 and 2. Correlations are made with baseline parameters of lipids, coagulation, and adjusted for potential confounding variables of tobacco use, pneumonia, and altered pulmonary function. An additional analysis of a subcohort, the above 400 controls, is performed looking at the outcome of their carotid IMT, a parameter of subclinical atherosclerosis, in relation to serologic results indicating a prior exposure to CMV, Chlamydia pneumoniae, and/or other pathogens approximately eight years preceding ultrasound testing. Both case-control and cohort analysis are stratified by levels of hemostasis and inflammation, including CRP, fibrinogen, Lp(a), and plasminogen-activator inhibitor-1. A separate nested substudy performed on peripheral blood mononuclear cells (PBMCs), prospectively collected from 80 cases and 80 controls, examines the host T-cell proliferative response to CMV and other pathogens in relation to disease and also searches for a chronic persistent infection with Chlamydia pneumoniae evidence by DNA detection.