Aspirin supplementation is less effective at inhibiting NO consumption in platelets from HF than from NF volunteers. Baseline NO consumption following a 14-day NSAID-free washout period of washed platelets was determined as described in “Patients, materials, and methods,” then subjects were randomly assigned to receive either aspirin or placebo in a crossover manner as described in “Patients, materials, and methods,” before repeat determinations of platelet NO consumption. (A-B) HF donors, (C-D) NF donors. (A) Representative trace showing NO consumption by platelets from one HF donor (i) at baseline, (ii) following aspirin supplementation, and (iii) after placebo, with 50 μM arachidonate added at arrow. (B) Cumulative data showing the effect of aspirin supplementation on HF platelet NO consumption rates (mean ± SEM, n = 6 separate donors; NS, not significant, Student unpaired t test). (C) Representative trace showing NO consumption by platelets from one NF donor (i) at baseline, (ii) following aspirin supplementation, and (iii) after placebo, with 50 μM arachidonate added at arrow. (D) Cumulative data showing the effect of aspirin supplementation on NF platelet NO consumption rates (mean ± SEM, n = 4 separate donors; *P < .02, Student unpaired t test).