MRS2179 is a competitive P2Y1 receptor antagonist (Kb = 100 nM) with no appreciable activity at P2Y2, P2Y4, or P2Y6 at concentrations up to 30 µM, or at P2Y12 and P2Y13. It inhibits ADP-induced platelet shape change and aggregation (pA2 = 6.55) in vitro a