Effects of heparin, aspirin and dipyridamole on thrombus formation on venous catheters.

Heparin, aspirin and dipyridamole were given alone or in combination to groups of sheep which had polyethylene catheters inserted into facial and saphenous veins. Animals were killed after 3 or 9 days. Neither aspirin nor dipyridamole reduced the amounts of thrombus on the catheters at autopsy. Heparin reduced thrombus only when sufficient was given to reduce blood coagulation.