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To define the long-term variability of serial coronary flow reserve (CFR) measurements in humans and to evaluate the influence of changes in heart rate, mean arterial pressure, and left ventricular preload on CFR, 45 patients with normal left ventricular function (38 cardiac allograft recipients, five patients with normal coronary arteries, and two patients with minimal coronary artery disease [less than 50% diameter stenosis]) were studied. CFR (ratio of peak hyperemic [h] to resting [r] coronary blood flow velocity [CBFV]) was measured with a 3F coronary Doppler catheter and intracoronary papaverine. Initial CFR measurements were highly correlated with repeat measurements obtained 11 +/- 0.6 months later (r = 0.95; mean absolute difference, 0.3 +/- 0.1; n = 17). Differences in CFR between studies were related to changes in heart rate (r = 0.61, p = 0.01) but not to changes in mean arterial pressure (r = 0.25, p = 0.33 …