RT4 cells that were pre-treated with anti-ACE2 antibodies were introduced to UFH. 100nM S1S2 was completely inhibited by UFH with an IC50 of 0.033U/ml, a measurement of the potency of an inhibitor (95% confidence interval 0.016-0.07). This potency value is well below the serum concentrations of UFH used to treat patients prophylactically and therapeutically.