The purpose of this study is to determine if Vitamin D supplementation helps prevent recurrent cardiovascular events, such as heart attack or stroke, in patients who have already experienced at least one cardiovascular event. This study will investigate if the addition of 150,000 international units of cholecalciferol (vitamin D3) by mouth every 2 months to a subject's medication regimen will prevent further cardiovascular events.

The purpose of this study is to determine if Vitamin D supplementation helps prevent recurrent cardiovascular events, such as heart attack or stroke, in patients who have already experienced at least one cardiovascular event. This study will investigate if the addition of 150,000 international units of cholecalciferol (vitamin D3) by mouth every 2 months to a subject's medication regimen will prevent further 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.