This study explores graft geometry and hemodynamics in a reproducible canine arteriovenous loop graft model of intimal-medial hyperplasia. Untapered 6 mm diameter polytetrafluoroethylene grafts (n = 10) were paired with 4 to 7 mm taper (n = 5) or 7 to 4 mm taper (n = 5) grafts for a 12-week period. Several hemodynamic variables were assessed at multiple locations, and venous intimal-medial thickness was measured at locations corresponding to the hemodynamic measurements. Color Doppler imaging demonstrated energy transfer out of the vessel in the form of perivascular tissue vibration. This was quantitated by the distance required for Doppler signal attenuation or volume of the detected vibration signal. Differences among graft types were noted for pressure, flow velocity, tissue vibration, and venous intimal-medial thickness. Hyperplasia was significantly decreased in 4 to 7 mm taper grafts. Stepwise deletion regression indicated volume of the vibration signal had a better correlation with venous intimal-medial thickness than any other variable (r 0.9, p less than 0.001). We conclude that graft geometry can have a significant impact on hemodynamic factors and venous intimal-medial hyperplasia in arteriovenous loop grafts. Flow disturbances appear to cause energy transfer through the vessel wall and into perivascular tissue. Kinetic energy transfer in the form of perivascular tissue vibration was quantitated in vivo and correlates strongly with venous intimal-medial thickness.