Is it true that heparin is able to break up clots that have already formed when treating pulmonary embolisms?

False-heparin cannot break up clots already formed but can prevent clots from increasing in size. heparin does this by inhibiting blood clotting processes. heparin contains a unique pentasaccharide sequence which binds antithrombin with high affinity. once bound, heparin acts as a catalyst by inducing a conformation change in antithrombin. after the conformational change, antithrombin deactivates clotting factor proteases including thrombin (iia), ixa, and xa thereby inhibiting clotting activity. heparin is not covalently bound to antithrombin, but is instead free to disassociate and bind to further antithrombin molecules. the presence of heparin therefore speeds this reaction 1000 fold compared to natural occurrence