Hemagglutinin V-5, abbriviated HGV-5, was a drug that Howard King of Biosyn worked on to stop dissolve blood clots in people with heart attacks. Initially tests on the drug were successful, but as more testing was done it proved to be failure.
King worked on the substance during his time at BioSyn and early tests of HGV-5 successfully dissolved platelet aggregation to an extreme degree. This made King the most promising researcher of the company, and BioSyn gave him his own laboratory and an operating budget of nearly half a million dollars. However, during preliminary testing of human subjects HGV-5 showed problems. It failed to dissolve clots in myocardial infarctions and pulmonary embolism. It also had bad side effects: gastrointestinal bleeding, skin rashes, and neurological problems.
Eventually, a test subject died of convulsions, putting testing on halt. In the weeks that followed Howard lost his laboratory and it became the lab for a Danish researcher developing an extract from the Sumatran yellow leech.