Endothelin ET(B) receptors mediate under normal physiological conditions vasorelaxation in coronary arteries. However, vasocontractile ET(B) receptors appear in coronary arteries of ischemic heart disease patients. Interestingly, organ culture of isolated coronary arteries also induces upregulation of vasocontractile ET(B) receptors. This study examines the early time course and mechanism behind upregulation of contractile ET(B) receptors in isolated rat coronary arteries during short-term organ culture.