• LVEF ≥ 45% judged by echocardiography during the screening epoch or within 6 months prior to screening visit

• Symptom(s) of heart failure for at least 30 days prior to screening visit and current symptoms of heart failure (NYHA functional class II-IV) at screening visit

• Objective evidence of cardiac structural and/or functional abnormalities consistent with the presence of LV diastolic dysfunction/raised LV filling pressures (left atrial enlargement and/or left ventricular hypertrophy) judged by echocardiography at screening epoch or within 12 months prior to screening visit

• Raised pro-BNP ≥ 125 pg/ml (sinus rhythm) or ≥ 300 pg/ml (atrial fibrillation (AF)).

• Body Mass Index (BMI) \< 40 kg/m2 at screening visit

• Female patients should either not be of childbearing potential, defined as postmenopausal for at least 1 year or surgically sterile, or of childbearing potential and practicing one of the following methods of contraception throughout the study and for 30 days after study completion: Hormonal contraception (oral contraceptives, contraceptive implant, injectable birth control, contraceptive patch, or vaginal ring) or intrauterine device

• Patients will have given written, informed consent and are able and willing to comply with the requirements of the study protocol