Coronary angiography is widely used to estimate coronary blood flow velocity, as in the TIMI frame count method. However, it is unknown to what extent the injection of dye elevates intracoronary pressure which may accelerate coronary blood flow velocity. In the present study, intracoronary pressure was measured during coronary angiography.In 25 patients with non-significant coronary lesions, assessed by fractional flow reserve measurement with a pressure guidewire, we recorded intracoronary pressure during dye injection for coronary angiography in the ostium of the coronary artery as well as distal to the lesion. There was a rise in mean intracoronary pressure during dye injection in both ostial and distal coronary arterial segments (from 90.8 +/- 17.2 mmHg to 96.8 +/- 18.5 mmHg and from 89.7 +/- 15.3 mmHg to 93.6 +/- 17.3 mmHg, respectively; p<0.001). Nevertheless, the absolute and relative increase in pressure was small (6.0 +/- 4.2 mmHg [6.7 +/- 4.9%] in the ostium, and 3.9 +/- 5.5 mmHg [4.2 +/- 5.7%] distally).In coronary arteries without significant stenosis, coronary angiography causes only a minor increase in intracoronary pressure. The limited impact of dye injection on intracoronary blood pressure confirms the value of coronary angiography for estimation of coronary flow velocity.