Antiplatelet agents, such as aspirin and P2Y12 inhibitors, are essential in the secondary prevention of cardiovascular disease . Despite effective treatment with these drugs, many patients still suffer ischemic events. This suggests the need for additional antiplatelet therapy. The P2Y1 receptor is a seven transmembrane G protein coupled receptor responsible for platelet shape change and reversible aggregation . Animal studies have shown that antagonists of the P2Y1 receptor, such as MRS2179, inhibit platelet aggregation . The effect of P2Y1 inhibition in man is not yet clear. To address this we characterised platelet function in human blood using a novel shear-mediated dynamic assay.