Microvascular thrombosis is known to play an important part in the cessation of flow seen in a flap following ischemia and revascularization. Its reversal, using thrombolytic therapy, is associated with higher rates of successful flap salvage. Although this procedure restores patency to the microcirculation, the damaged endothelial cell layer remains highly thrombogenic and a definite risk of rethrombosis exists in the early period of reperfusion. In an inferior epigastric flap model in a rat, we investigated the effect of additional heparin (subcutaneous and intravenous administration) following a standardized urokinase washout (100,000 iu) of the ischemic flaps. Flap survival was assessed at 1 week and morphological changes in the microcirculation were observed using electron microscopy. Results showed a significant increase in flap survival in the group receiving intravenous heparin following urokinase washout and suggest that systemic heparin may play a beneficial role in the early reperfusion period following thrombolytic flap salvage.