A Study of LY3540378 in Participants With Worsening Chronic Heart Failure With Preserved Ejection Fraction (HFpEF)

Inclusion Criteria: * Experienced an index event, defined as a recent hospitalization for HF requiring ≥1 bolus doses of intravenous diuretics or an out- of- hospital encounter (for example, Emergency Room, clinic visit, infusion clinic, etc.) for HF requiring ≥1 bolus doses of intravenous diuretics. * Documented LVEF of ≥50% within 12 months prior to screening; as measured by echocardiography, radionuclide ventriculography, invasive angiography, magnetic resonance imaging (MRI), or computerized tomograph (CT). * Evidence of documentation of LVEF of ≥50% may also include participant medical records, discharge notes or a referral letter from the participant's physician or referring physician that details the participant's medical history. * Had evidence of clinical HF syndrome consisting of hospitalization for worsening heart failure (WHF) with intravascular volume overload (the index event), as determined by the investigator, based on appropriate supportive documentation at randomization, and defined by ≥2 of the following: * dyspnea * jugular venous distention * pitting edema in lower extremities (\>1+) * ascites * pulmonary congestion on chest X-ray * pulmonary rales AND participant received treatment with IV diuretics. OR * Treatment for an urgent visit outside of of being hospitalized with WHF and intravascular volume overload (the index visit) requiring treatment with IV diuretics (defined as ≥2 IV doses) such as in the outpatient setting/emergency room/observation unit/infusion clinic with a clinical response within the past 2 weeks prior to randomization. Urgent visit is defined as an unplanned visit for HF defined by ≥2 of the following: * dyspnea * jugular venous distention * pitting edema in lower extremities (\>1+) * ascites * pulmonary rales on lung examination. * NT-proBNP (\>300 \[sinus rhythm\] or 600 pg/mL \[atrial fibrillation or atrial flutter\] OR BNP (\>100 \[sinus rhythm\] or 200 pg/mL \[atrial fibrillation or atrial flutter\]) at screening. * eGFR of \>20 mL/min/1.73 m² at V1 (screening; determined by local laboratory), derived from serum creatinine values, age, and sex based on the CKD-EPI equation. Exclusion Criteria * Prior documentation of low ventricle ejection fraction (LVEF) ≤45% in the past 12 months. * Have had acute coronary syndrome or percutaneous coronary intervention, coronary artery bypass graft, cardiac mechanical support implantation, within 3 months prior to V2. (randomization), - or any other cardiac surgery planned during the study. * Have had left ventricular assist device (LVAD) or cardiac transplantation or have cardiac transplantation planned during the study. * Have hypertrophic cardiomyopathy (obstructive or nonobstructive), restrictive cardiomyopathy, active myocarditis, constrictive pericarditis, cardiac sarcoidosis, known amyloid cardiomyopathy, or inherited cardiomyopathy. * Have a chronic pulmonary/lung disease (COPD), (pulmonary arterial hypertension, etc) as defined by chronic oxygen dependence. Night-time oxygen is not exclusionary. * Uncorrected thyroid disease.