Background Dyslipidemia is common in heart failure with preserved ejection fraction. Sacubitril/valsartan improves glycemic control and augments natriuretic peptide signaling, providing mechanisms by which sacubitril/valsartan may affect serum lipids. However, empiric data on these effects are lacking. Methods and Results We analyzed 4774 participants from PARAGON-HF (Prospective Comparison of Angiotensin Receptor-Neprilysin Inhibitor With Angiotensin-Receptor Blockers Global Outcomes in Heart Failure With Preserved Ejection Fraction) with available screening lipids. During follow-up visits, we analyzed the treatment effect on lipid levels and assessed for interaction by baseline lipid levels. At the 16-week visit, we adjusted these treatment effects for the change in several biomarkers (including hemoglobin A1c and urinary cyclic guanosine monophosphate/creatinine [a biomarker of natriuretic peptide activation]). The average age was 73±8 years, 52% were women, 43% had diabetes mellitus, and 64% were on statin therapy. Compared with valsartan, sacubitril/valsartan reduced triglycerides -5.0% (95% CI, -6.6% to -3.5%), increased high-density lipoprotein cholesterol +2.6% (95% CI, +1.7% to +3.4%), and increased low-density lipoprotein cholesterol +1.7% (95% CI, +0.4% to +3.0%). Sacubitril/valsartan reduced triglycerides most among those with elevated baseline levels (triglycerides≥200 mg/dL) (P-interaction<0.001), and at 16 weeks by -13.0% (95% CI, -18.1% to -7.6%), or -29.9 (95% CI, -44.3 to -15.5) mg/dL, in this group. Adjusting for the change in urinary cyclic guanosine monophosphate/creatinine significantly attenuated treatment effects on triglycerides and high-density lipoprotein cholesterol, but not low-density lipoprotein cholesterol, while adjusting for other biomarkers did not significantly alter the treatment effects. Conclusions Sacubitril/valsartan significantly reduces triglycerides compared with valsartan, an effect that was nearly threefold stronger in those with elevated baseline triglycerides. Modest increases in high-density lipoprotein cholesterol and low-density lipoprotein cholesterol cholesterol were also observed with therapy. The underlying mechanism(s) of changes in high-density lipoprotein cholesterol and triglycerides are related to sacubitril/valsartan's effects on natriuretic peptide activity. Registration URL: https://www.clinicaltrials.gov; Unique identifier: NCT01920711.