Heparin therapy is contra-indicated in patients who are hypersensitive to the drug. It should not be used in the presence of actual or potential haemorrhagic states, eg. haemophilia, ascorbic acid deficiency or increased capillary fragility; threatened abortion; immediate postpartum period, subacute bacterial endocarditis; severe hypertension; gastric or duodenal ulcers; advanced renal or hepatic disease; during and immediately after spinal or major surgery, especially those involving the brain, eye or spinal cord.