Background: The ratio of ucGMP (urinary cyclic guanosine monophosphate) to BNP (B-type natriuretic peptide) is thought to reflect the responsiveness of tissues to natriuretic peptides. Methods: We examined the relationship between ucGMP/BNP ratio and clinical outcomes, the effect of sacubitril/valsartan, compared with enalapril, on the ucGMP/BNP ratio, and the efficacy of sacubitril/valsartan on clinical outcomes according to baseline ucGMP/BNP ratio in PARADIGM-HF trial (Prospective Comparison of ARNI With ACEI to Determine Impact on Global Mortality and Morbidity in Heart Failure). ucGMP/BNP ratio was available at baseline (N=2031), 1 month (N=1959), and 8 months after randomization (N=1746). The primary outcome was a composite of heart failure hospitalization or cardiovascular death. Results: Compared with the lowest tertile of baseline ucGMP/BNP ratio, patients in the higher tertiles had a lower risk of the primary outcome (tertile 1, reference; tertile 2, hazard ratio 0.57 [95% CI, 0.45-0.71]; tertile 3, hazard ratio, 0.54 [0.43-0.67]). Compared with baseline, the ucGMP/BNP ratio at 1 month and 8 months after randomization was higher with sacubitril/valsartan than with enalapril: ratio of geometric mean ratios at 1 month, 1.38 (95% CI, 1.27-1.51) and 8 months, 1.32 (95% CI, 1.20-1.45), and this difference was consistent across tertiles of ucGMP/BNP ratio at baseline (Pinteraction=0.19 and 0.91, respectively). The effect of sacubitril/valsartan, compared with enalapril, was consistent across tertiles of ucGMP/BNP ratio at baseline for all outcomes (Pinteraction ≥0.31). Conclusions: In patients with heart failure and reduced ejection fraction, higher ucGMP/BNP ratio was associated with better outcomes. Sacubitril/valsartan increased the ucGMP/BNP ratio, compared with enalapril, and the effect of sacubitril/valsartan on clinical outcomes was not modified by baseline ucGMP/BNP ratio.