These specialized tracings illustrate several important patterns of coronary blood flow velocity that may occur in patients during diagnostic cardiac catheterization. Recent advances in catheter methodologies permit easy measurement of coronary blood flow during routine coronary angiography. At the current time, measurement of coronary blood flow velocity remains a research technique but is of continuing interest in clinical syndromes of atypical angina, myocardial hypertrophy and infarction, early transplant rejection, or premature (subangiographic) atherosclerosis in some patients. A later hemodynamic rounds will examine the effects of coronary blood flow velocity and various hyperemic stimuli to assess coronary vasodilatory reserve.