Serial quantitative angiographic studies are frequently employed to assess the effect of dietary or mechanical interventions on the severity of coronary artery stenosis and angiographic conditions that may alter coronary diameter via changes in pressure need to be avoided. The purpose of this study was to investigate the extent of hemodynamic changes introduced during the injection of radiographic contrast into the coronary ostium. A linear resistance model was developed to simulate this event for different rates of injection (2-6 ml/sec) and resistance ratios (Rcor/Rcath= 40 and 80). The results show an increase in coronary pressure between 7 and 44 mmHg at the time of injection, which depends primarily on the injection rate and the resistance posed by the guiding catheter in the coronary ostium. These data are consistent with earlier experimental results and point to the importance of standardizing contrast injections for QCA studies.