Urinary 11-dehydro-TXB₂excretion is not inhibited by aspirin in HF subjects. At baseline, and following aspirin or placebo supplementation, urine samples were obtained and analyzed for 11-dehydro-TXB₂ using GC-MS in NM (n = 5), HF (n = 6), and NF (n = 4) samples (mean ± SEM; *P < .03, Student unpaired t test).