Background: Left ventricular mass and left ventricular mass index (LVMI) is an index reflecting the thickness of the cardiac muscle, and the E/e' ratio is a specific indicator for identifying increased left ventricular filling pressure. Limited data exist regarding the prognostic value of incorporating left ventricular mass index in heart failure with preserved ejection fraction (HFpEF). Aim: This study aimed to assess diagnostic value of LVMI at rest versus diastolic stress echo results in patients with HFpEF. Patients and methods: This study is a cross sectional descriptive study. In our study, we investigated 80 patients with unexplained exertional dyspnea with normal resting LV filling pressure at rest. Some of these patients may show elevated LV filling pressure with exercise. The current guidelines recommend to do diastolic stress echocardiography for those patients. All patients underwent complete resting echocardiography including assessment of diastolic dysfunction using the recommended 2016 guidelines and left ventricular mass index. Then we did diastolic stress echocardiography for all participants and the result of diastolic stress echocardiography was compared with the  resting LVMI results.