OBJECTIVES: The direct determinants of coronary flow are lumen area and blood flow velocity, however the precise mechanisms that control these factors are not fully understood. The aim of the present study was to assess by which mechanisms lumen area and coronary flow velocity interact with hemodynamic and morphometric factors, thereby influencing coronary flow. METHODS: Intracoronary Doppler and ultrasound measurements were performed in 28 patients without coronary lumen irregularities. Flow velocity and lumen cross-sectional area were measured in the proximal segments of all 3 coronary arteries. Global lumen cross-sectional area and global flow were obtained by adding up the values of all 3 coronary arteries. Left ventricular mass was assessed by echocardiography. Stress-mass-heart rate and pressure-rate-product reflecting myocardial oxygen demand were calculated. Results: Global coronary flow increased during adenosine-induced hyperemia from 197±72ml/min to 637±204ml/min (p<0.001). Global coronary flow closely correlated with the stress-mass-heart rate product (r=0.62; p<0.001). Looking at the two constituents of flow separately, global coronary cross sectional area was closely related to left ventricular muscle mass (r=0.61; p<0.001), while mean coronary flow velocity at rest showed a strong linear relation with the pressure-rate product (r=0.64; p<0.001). There was no interaction between cross-sectional area and blood flow velocity in any of the coronary vessels. CONCLUSION: Coronary lumen size and flow velocity --the two determinants of coronary flow -- are principally determined by different physiologic factors. Long-term flow adaptation is achieved by an increase in coronary lumen size, while short term myocardial oxygen requirements are met by changes in resting flow velocity.