 Coronary artery disease is a leading cause of morbidity and mortality in our society. It is initiated by the dysfunction of the lining of coronary arteries. There are several repair mechanisms that are now thought to involve circulating endothelial progenitor cells that are mobilized from the bone marrow and home to sites of endothelial injury. We hypothesize that aging is associated with reduced vascular injury induced endothelial progenitor cell activity, resulting in impaired vascular repair and increased coronary heart disease events. 96 patients with stable coronary artery disease will be enrolled in this study. They will undergo either angiography alone or angiography and angioplasty. Their venous blood will be collected immediately prior to the procedure and 20-24 hours after their procedure. The number of endothelial progenitor cells will be assessed based on their ability to form colonies and also to migrate under the influence of certain growth factors. These values will be compared between both samples. All the patients will also be contacted at 6 months, 2 and 5 years after their participation in the study and the clinical outcomes of their coronary artery disease will be correlated with the number of those aforementioned cells. 