Why warfarin used in long term treatment of deep venous thrombosis? why not heparin?

Oral administration.: Warfarin is available in an oral dose and is given on a daily basis. Its effects lasts 24 hours and takes about 72 hours to clear from your system. Heparin is given either intravenously or subcutaneously and requires dosing every 4 to 8 hours or continuously depending on the method of administration. Long term anticoagulation is easier and better tolerated with an oral medication.

Pill: Warfarin is a pill, while heparin is iv. Newer anticoagulants have been recently used. They come in a subcutaneous injection or a pill form. Ask your doctor about options other than the above 2.