Acute Effect of Systemic Stress on Measured Blood Concentrations of 25 (OH) Vitamin D (ASSESS-D)

Inclusion Criteria:

1. Male or female >= 18 years of age
2. Ability to understand and sign a written informed consent form, which must be obtained prior to initiation of any study procedures
3. Subject is scheduled for elective open heart surgery at Intermountain Medical Center
4. Subject is relatively stable as assessed by the Principal Investigator

Exclusion Criteria:

1. Inability or refusal of the patient and/or the patient's legally acceptable representative to provide written informed consent for any reason.
2. History of previous vitamin D supplementation > 1,000 units of vitamin D3 per day within the past three months.
3. Evidence of hypercalcemia on screening labs (> 10.5 milligrams per deciliter of blood).
4. Any scheduled cardiac surgical procedure that does not require open thoracotomy (the reason for this exclusion is that the study design requires that the patients will undergo a significantly stressful procedure, which can be generally guaranteed if the patient undergoes open thoracotomy).
5. Known allergic reaction or other intolerance to oral vitamin D3.
6. Pregnant and/or lactating women and women of child bearing potential who are not using acceptable means of contraception. Women of childbearing potential must be using adequate measures of contraception (as determined by the Principal Investigator) to avoid pregnancy and should be highly unlikely to conceive during the study period. Women of childbearing potential must have a negative pregnancy test at screen.
7. Subject participation in previous investigational interventional studies within 30 days of the current study.
8. Other conditions that in the opinion of the Principal Investigator may increase risk to the subject and/or compromise the quality of the clinical trial.