The effect of aspirin on platelet aggregation caused by simultaneous stimulation of the G_i and G_z pathways. Top panel contains aggregation tracings of non–aspirin-treated washed human platelets, while the bottom panel contains aspirin-treated washed human platelets. Where noted, the antagonist 100 μM MRS2179 was added 1 minute prior to the addition of other agonists. The agonists 100 nM 2-MeSADP and 10 μM epinephrine were added simultaneously where noted. The arrows indicate addition of agonists. All samples are performed in the presence of 1 mg/mL fibrinogen. Tracings are representative of data obtained from 3 different donors.