After intravenous or subcutaneous injection heparin is extensively bound to plasma proteins. The half-life of heparin depends on its dose and route as well as the method of calculation and is subject to wide inter- and intra-individual variation; a range of 1 to 6 hours with an average of 1.5 hours has been cited. It may be slightly prolonged in renal impairment, decreased in patients with pulmonary embolism, and either increased or decreased in patients with liver disorders. Heparin is taken up by the reticuloendothelial system. It is excreted in the urine, mainly as metabolites, although after large doses up to 50% may be excreted unchanged.
Martindale Complete Drug Reference. Pharmaceutical Press (via Medicines Complete), last reviewed 2011-11-15

Heparin is not eliminated enzymatically nor by glomerular filtration or renal tubular secretion. In all likelihood, the anticoagulant is transferred to reticuloendothelial cells, which may also provide the means for its degradation.
Estes JW. Clinical pharmacokinetics of heparin. Clin Pharmacokinet 1980; 5: 204–20.

After either subcutaneous or intravenous injection heparin is distributed primarily within the intravascular space. A short distribution phase is seen which is thought to correspond to endothelial cell binding and internalisation. The disposition curve for unfractionated heparin has a unique concave-convex shape which is the result of combined saturable and nonsaturable elimination mechanisms. The nonsaturable elimination mechanism is renal and is the primary route of elimination for low molecular weight heparins.
Kandrotas RJ. Heparin pharmacokinetics and pharmacodynamics. Clin Pharmacokinet 1992; 22: 359–74.