The aims of the present study were to quantitate myocardial perfusion and capillary permeability in the human heart by means of the single-injection, residue detection method using a mobile gamma camera. With this method, the intravascular mean transit time and the capillary extraction fraction (E) can be determined in one experiment and in the same myocardial region. Eighteen patients with a history of chest pain episodes and angiographically normal coronary arteries were studied after intracoronary bolus injections of 99mTc-DTPA during elective coronary angiography. Two measurements were performed at a 15-min interval during resting conditions, and a third measurement was made during atrial pacing. Regions of interest were drawn in the left anterior descending (LAD) and the circumflex (CX) coronary artery perfusion beds. Sources of variation in plasma flow rate (fpl), E, and the calculated capillary permeability area product (PS) were determined. Spontaneous 15 min variations (mean of two values) for the LAD and the CX territory, respectively, gave a mean fpl(LAD) of 74.2 (measurement 1) and 77.8 ml.(100 g.min)-1 (measurement 2) (SD of the difference 7.5 ml.(100 g.min)-1) and fpl(CX) of 82.7 and 92.1 ml. (100 g.min)-1, respectively (SD of the difference 16.1 ml.(100 g.min)-1), and E(LAD) was 51.0 and 55.7%, respectively (SD of the difference 8.4%), and E(CX) was 52.9 and 50.4%, respectively (SD of the difference 5.9%). During atrial pacing, the rate-pressure product increased by 97%, and in the LAD area fpl increased by 46% (p <0.05), E decreased by 6% (NS), and PS increased by 39% (NS), whereas in the CX region flow increased by only 9% (p <0.01), E decreased by 15% (p <0.05), and PS decreased by 15% (NS) compared with baseline values. Both the spontaneous variation and the observer variation are low. The reduced vasodilator response in the CX region in combination with the decrease in E, which reduce the supply of nutrients, may play a role in the symptoms of these patients.