Heparin inhibits Xa by: (A) Blocking vitamin K mediated activation of Xa, (B) Activating Antithrombin III, (C) Direct breakdown of Xa, (D) Blocking P2 Y12 receptor of ADP
Answer is B. Heparin contains pentasaccharide unit that activates Antithrombin III & inhibits factor Xa (Thus it is a indirect thrombin inhibitor).
Unfractionised heparin also contains a heteropolysaccharide unit that inhibits factor II a.
LMWH lacks this heteropolysacchoride unit and therefore inhibitors factor Xa only.