Tendons exhibit viscoelastic properties reflected by a non-linear force-deformation relation and energy loss upon stretching and release. It is known that tendons change mechanical properties acutely after loading, which is attributed in part to tissue viscosity. Although sparse, tendons are vascularized but whether blood flow or viscous pressure influences the mechanical properties acutely is unknown. Human cadaver specimens with intact vessels can be perfused at physiological pressure, which combined with tensile testing may yield information of the role of tissue perfusion on tendon function. PURPOSE: To examine if tissue perfusion influences the mechanical properties of tendons during loading and unloading. METHODS: Four fresh intact cadaver hand specimens were sectioned proximal to the processus styloideus. The a. ulnaris was cannulated to enable saline perfusion of the hand at physiological pressure. The flexor digitorum profundus tendon of the middle finger was mounted in a tensile testing device, and distally, the tip of the intact finger was clamped allowing repetitive loading of the tendon. Four series of 10 tendon loadings were conducted: 2 with perfusion and 2 series without. Series were separated by 5 min with or without perfusion. Subsequently the specimens were perfused with ink and upon dissection the vincular arteries were colored indicating that the tendons had received perfusion. RESULTS: Hysteresis was reduced over all series of loadings but the reduction was greater when the tissue was not perfused (40%) compared to loading series with perfusion (30%, P<0.05). Hysteresis recovered in rest periods, but recovery was doubled during perfused rest compared to rest without perfusion. Tendon stiffness increased through loading series but perfusion did not significantly influence the increase. However, reduction of tendon stiffness during rest periods was greater with perfusion (9%) compared to no perfusion (3%, P<0.05). CONCLUSIONS: Despite non physiological conditions the present data indicate that tissue perfusion may influence the mechanical properties of the force bearing tissues both with respect to stiffness and ability to store and release energy. It should be noted that a limited number of cadavers were available suggesting that caution be taken when data are interpreted.