100 subjects with angiographically documented CAD and Vit D deficiency will be randomized to 50,000 IU oral ergocalciferol (active treatment group) or placebo (delayed intervention group) once a week for 12 weeks. The investigators will measure endothelial function at randomization and week 12 using RH-PAT and serologically measured adhesion molecules (s-VCAM, s-ICAM, soluble e-selectin). Changes in levels of plasma cytokines and chemokines representing a T-cell activation pathway (IL-12, IFN-g and CXCL-10 - "IFN-g axis") the investigators have linked to coronary atherogenesis (independent of CRP) and poor CV outcomes, will be measured over the 12 week study period. Given published evidence showing that Vit D can influence this T- cell pathway, specific aim 2 will add mechanistic insights to this proposal. High sensitivity C-reactive protein (hs-CRP) will be measured as it is a well established traditional marker of inflammation in CAD and has also been linked to Vit D status.