BACKGROUND The present study was designed to evaluate the role of tachycardia-induced dynamic coronary artery diameter changes in the development of myocardial ischemia. METHODS Coronary angiography at rest and during atrial pacing-induced myocardial ischemia was performed in 22 patients. The diameter of the proximal and the corresponding distal coronary artery segments at rest and during pacing was measured using quantitative coronary angiography. Plasma levels of noradrenaline, adrenaline, dopamine and endothelin were determined in a subset of 14 patients in blood drawn from aorta and coronary sinus at rest and during pacing. RESULTS Luminal diameter in normal proximal and distal segments increased, respectively, from 2.93 +/- 0.34 and 1.40 +/- 0.04 mm at rest to 3.03 +/- 0.25 and 1.58 +/- 0.07 mm during atrial pacing. The diameter of the proximal coronary artery segments with significant concentric stenosis decreased from 1.28 +/- 0.4 mm at rest to 0.95 +/- 0.34 mm during pacing, whereas segments with either significant eccentric or non-significant stenosis did not change significantly. A correlation was found between the noradrenaline level in the coronary sinus and the distal coronary artery diameter. CONCLUSIONS A decrease in diameter of coronary artery segments with concentric stenosis during tachycardia might contribute to the development of myocardial ischemia. Some of the dynamic coronary artery changes may be influenced by the plasma level of noradrenaline. No evidence was found to suggest that dynamic changes in the diameter of proximal segments are related to the changes in diameter of the corresponding distal segments.