• Change in minimum luminal diameter from baseline assessed by Quantitative Angiography
  
• Coronary Flow Reserve (max/basal CBFV) assessed by coronary Doppler Wire
  
• Correlation between the change in culprit epicardial artery stenosis MLD and atherectomy specimen ET-1 content assessed by immunochemistry
  

Inclusion Criteria:

Adult men and women between the ages of 18 to 75 years will be enrolled and categorized into one of 4 groups. The categories are defined below:

• Control patients characterized by chest pain and angiographically normal coronary arteries.
• Chronic stable angina patients who describe a history of exertional chest pain which is unchanged in frequency over the preceding month, and who have at least a 70% stenosis in a coronary artery.
• Unstable angina patients who describe chest pain at rest or with minimal exertion over the preceding 2 weeks, and who have an identifiable culprit stenosis in a coronary artery.
• Cardiac transplant recipients who are undergoing routine annual surveillance cardiac catheterization.

Exclusion Criteria:

Patients with the following will be excluded from the study:

• Angiographic exclusion criteria: *Left main coronary artery disease or severe triple vessel disease; *Unstable angina without any identifiable culprit lesion.
• Severe left ventricular dysfunction (ejection fraction < 40%) or clinical cardiac failure.
• Nitroglycerin required in the preceding 4 hours prior to the investigation.
• Severe renal, hepatic or hematologic abnormalities.
• Inability to obtain written informed consent.