Atherosclerosis, or hardening of the arteries, is the underlying disease responsible for the vast majority of cardiovascular morbidity and mortality and afflicted over 30 million Americans in 2005. While the prevalence of atherosclerosis is similar in women and men, women enjoy a ~5-10 year lag in onset of cardiovascular events compared to men. After menopause, a state defined by marked reduction in ovarian hormone production, the incidence of events such as heart attack and stroke caused by atherosclerotic plaque rises up to threefold regardless of age range. This has prompted numerous investigations of hormone therapy (HT) to lower cardiovascular risk to premenopausal levels. Therapeutic trials, however, have not realized a cardiovascular benefit; in fact, initiating HT in large randomized trials did not decrease and possibly increased cardiovascular risk. Studies of coronary heart disease prevention have shown mixed results using estrogen alone vs. estrogen plus progestin, while studies of stroke prevention have consistently shown increased risk with HT. Clearly, different therapeutic interventions warrant consideration. This proposal seeks to investigate a novel perspective using longitudinal clinical studies in women at risk of atherosclerosis. The studies involve a new noncontrast, noninvasive MRI method with blood tests that measure cholesterol, hormone levels, and inflammation.