This is a research study evaluating possible causes of chest pain (or an anginal equivalent, such as fatigue resulting in a decrease in exercise tolerance, shortness of breath, or back, shoulder, neck, or jaw pain) in people with no evidence of significant coronary artery disease on their coronary angiogram (pictures of the blood vessels in the heart). The purpose of the research study is to determine if there is diffuse atherosclerosis (plaque) not appreciated by angiography, or if the coronary endothelium (lining of the blood vessels in the heart) and/or microcirculation (small vessels in the heart that are not easily seen with an angiogram) are not functioning properly in those who have chest pain (or an anginal equivalent), but normal coronary arteries on angiography. Specifically, we are interested if these findings are more common in women than men.