X-ray coronary angiography is widely used to determine the presence of a stenosis. This paper discusses an approach towards the detection of the functional severity of a stenosis using the relative velocity of the contrast agent. The velocity of the contrast is measured using the arrival time at several locations on a coronary artery. This is done by placing multiple Regions Of Interest(ROI) equally spaced on the artery. The location of these ROIs varies in time because of the cardiac motion. Therefore, an artery tracing and tracking algorithm is used to estimate the location of the ROIs in time. The arrival time of the contrast can be estimated by measuring the image intensity in these ROIs. Using the arrival times in several ROIs, a qualitative velocity can be estimated. Altering the velocity of the blood pharmacologically, by inducing hyperemic conditions, results in a qualitative change in velocity detected by the algorithm. 1 No change in velocity may indicate a severe flow limiting stenosis.