Chronic and acute hypertension have multiple untoward effects on the coronary circulation, several of which may either mimic or markedly worsen the clinical manifestations of coronary artery disease. Early after the onset of left ventricular hypertrophy secondary to hypertension, coronary vasodilator reserve is significantly impaired. During cardiac hypertrophy secondary to hypertension, the coronary arteries fail to enlarge in concert with ventricular enlargement. This failure results in a relative decrease by approximately 50% in the ratio of epicardial vessel diameter to the mass of myocardium perfused. The lower range of coronary subendocardial autoregulation is altered by chronic renovascular hypertension. A variety of vascular smooth muscle homeostatic mechanisms are abnormal in genetic models of hypertension, as is endothelium-dependent vascular relaxation. Acute hypertension may enhance constriction to serotonin, most likely through the release of potent vasoconstrictor substances from leukocytes and platelets that adhere to the endothelium as a result of endothelial damage. Finally, many of the consequences of myocardial infarction are worsened in the setting of hypertension and left ventricular hypertrophy.