 Following the research protocol, the patient will undergo appropriate coronary intervention as dictated by the clinical situation. If coronary atherectomy is required for clinical indications, then the specimen extracted by this procedure will be sent for specific analysis of endothelin-1 content. A correlation between the amount of endothelin at the culprit stenosis and the response to the endothelin antagonist can then be examined. In cardiac transplant recipients, endomyocardial biopsies are also routinely obtained for clinical purposes at the time of catheterization. One of these specimens will be used for ET-1 immunoreactivity analysis. A total of 2 teaspoons of blood will be taken and frozen for analysis. 