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Figure 3 Whole-blood impedance aggregometry: Protocol 3. (A) Original recordings of in vitro platelet aggregation (i.e., increase in impedance) in blood aliquots exogenously treated with sildenafil, the adenosine A₂ agonist CGS 21680, sildenafil + CGS 21680, and no drug (control). Arrows indicate addition of collagen (10 µg); bar = 2 min. (B) % Change in impedance (mean ± SEM) seen in CGS 21680-treated aliquots versus paired "no drug" samples. Data were obtained at baseline and after dose 2 in two vehicle-treated and two sildenafil-treated dogs. Black bars indicate controls; white bars indicate sildenafil.