Background: Heart failure with preserved ejection fraction (HFpEF) is a global public health epidemic that accounts for half of the heart failure cases. Various therapeutic approaches have been tested to block the activation of the Renin-Angiotensin System (RAS), including AT1R blockers (ARBs), Angiotensin-Converting Enzyme (ACE) inhibitors (ACEi), and direct renin inhibitors (DRIs) with modest to negligible benefits. The discovery of ACE2, a novel homolog of ACE, has advanced our understanding of the RAS. ACE2 is a monocarboxypeptidase that degrades Ang II into Ang-(1-7), which works via the activation of the Mas receptor. It has been well understood that the actions of Ang-(1-7) attenuate cardiac remodeling, production of ROS, and cardiac fibrosis. Objective: To determine the therapeutic role of Ang-(1-7) in HFpEF and identify the molecular mechanism related to its action. Methods and Results: To generate a murine model of HFpEF, male WT mice (n=24) were subjected to HFD in addition to eNOS inhibition with L-NAME (0.5 g l-1 in drinking water), as previously described. The control group (n=12) received chow diet and normal tap water. The murine model of HFpEF was validated using the non-invasive transthoracic echocardiography and invasive pressure-volume (PV) loop analyses, which exhibited diastolic dysfunction as well as cardiac hypertrophy. To evaluate the effects of Ang-(1-7) on HFpEF, animals were administered with either saline (n=12) or Ang-(1-7) (n=12) (24 μg/kg/day) for four weeks. Ang-(1-7) treatment improved diastolic function by reducing LVEDP (Ctrl: 8.267±1.254; HFD+L-NAME: 17.64±1.925; Ang-(1-7): 9.100±1.578) and Tau value (Ctrl: 7.365±0.5752; HFD+L-NAME: 9.224±0.3569; Ang-(1-7): 7.381±0.3041). Furthermore, Ang-(1-7) reduced cardiac hypertrophy by reducing the phosphorylation level of MAPK ERK 1/2 (Ctrl: 0.9074±0.1088; HFD+L-NAME: 1.212±0.1369; Ang-(1-7): 0.5615±0.1502) and increasing the phosphorylation level of AMPK (Ctrl: 0.1502±0.1502; HFD+L-NAME: 0.6127±0.06414; Ang-(1-7): 0.7852±0.1006). Ang-(1-7) treatment also reduces cardiomyocytes’ size and decreases interstitial fibrosis, as indicated by WGA and PSR staining. Conclusion: Ang-(1-7) treatment attenuated the development of HFD+L-NAME-induced HFpEF, reduced cardiac hypertrophy, and improved metabolic function.