Our main hypothesis is that EPC function is impaired in some populations with high cardiovascular risk as a result of reduced eNOS-dependent NO production.

To determine if a correlation exists between EPC function and eNOS-dependent NO production in EPCs from populations with high versus low cardiovascular risk:

1. High and low cardiovascular risk subjects will be identified based on age or history of cardiovascular disease. Endothelial function will be measured by ultrasound.
2. EPCs will be isolated from peripheral blood of these subjects. EPC function will be assessed by measuring adhesion to endothelium, migration, proliferation, and differentiation, and compared to their expression and activity of eNOS.

Inclusion Criteria:

• Willing and able to give written informed consent and comply with study requirements
• Adult of 18 years or older
• Subjects willing to provide blood and tissue samples

Exclusion Criteria:

• Failure to give informed consent.
• Those unable to consent for themselves.
• Those who cannot read English.
• Patients on Viagra, Levitra, or Cialis
• Patients with malignant disease
• Patients with hematological abnormalities
• Patients with fevers of unknown origin
• Severe comorbidity or alcohol/drug dependence
• Women who are post-menopausal and on hormone replacement therapy, or premenopausal and on birth control pills (premenopausal women will be screened verbally and then by assay of LH and FSH levels in blood samples to identify women in the follicular phase of their menstrual cycle, to reduce variability)

Population in both low and high risk groups should represent the general population.