Role of Vitamin D in Secondary Prevention of Cardiovascular Events

Inclusion Criteria: * Male or female of age \> 19 years at the time informed consent is signed. * Subject with a diagnosis of unstable angina (with Thrombolysis in Myocardial Infarction (TIMI) score of greater than or equal to 3) / NSTEMI or STEMI,or documented coronary artery disease defined as at least one coronary artery with \> 50% occlusion * Subject who is able to come back to our clinic for follow up visits for at least 1 year after enrollment. Exclusion Criteria: * Subject is on treatment with either phenytoin or phenobarbitol or orlistat (since these medications may cause vitamin D deficiency). * Subject who needs two or more steroid bursts per year for other co-morbid conditions (since steroids may impair vitamin D metabolism). * Subject is on an investigational drug, which is a new drug class and not part of standard ACS protocol. * Subject is taking supplements of vitamin D with doses \>400 IU/day. * Subject has hypersensitivity to vitamin D products. * Subject has history of systemic lupus erythematosus (since vitamin D deficiency is common in this group27). * Subject has history of sarcoidosis (since they have hypercalcemia and high levels of vitamin D28) * Subject has history of renal stones. * Subject has hypercalcemia, which is defined as serum calcium levels \>10.6 mg/dl, at the time of screening. * Subject has end stage renal disease, defined as either chronic kidney disease stage V or requiring dialysis (since these patients have altered vitamin D and calcium metabolism). * Subject has systemic disease (including terminal cancer, cirrhosis, end stage COPD etc.,) with reduced (\<12 months) life expectancy. * Subject has a history of psychiatric illness/condition that would interfere with his/her ability to understand or complete the requirements of the study. * Subject has any condition that in the opinion of the investigator places the subject at an unacceptable risk as a participant in this study. * Subject is pregnant.