In recent years, a new method to measure transverse blood flow, based on the decorrelation of the Radio Frequency (RF) signals has been introduced. In this paper, we studied the decorrelation characteristics of transverse blood flow using an intravascular ultrasound (IVUS) array catheter by means of computer modeling. Blood was modeled first as randomly located point scatterers and second as aggregates moving across the ultrasound beam. Next, spread of flow and flow gradient were simulated. IVUS flow measurements were used to study the influence of the ring-down size on flow measurements. Coronary Flow Reserve (CFR) was computed from this data and from a calibrated Transonic flowmeter. The decorrelation pattern for point scatterers, for aggregates and for non-homogeneous flow is in agreement with theoretical predictions from sound field calculations. Underestimation of flow occurs by the ring-down obscuring but good agreement between IVUS and flowmeter CFR was found.