The Effects of Active VItamin D on Left Atrial Volume Index

Inclusion Criteria: * Sign informed consent. * Willing and able to adhere to all study-related procedures, including study medication regimen. * ≥ 18 years old. * Previous clinical diagnosis of heart failure with preserved ejection fraction: NYHA Class II-IV. * Satisfy these echocardiographic criteria within the last year: Left ventricular ejection fraction ≥ 50%, cardiac magnetic resonance or ventriculogram; Left atrial size ≥ 4 cm in long axis or \> 5.2 cm in four chamber length; Septal wall thickness \> 1.2 cm (females) or 1.3 cm (males); Doppler evidence of moderate or severe diastolic dysfunction (≥ Grade II) by transmitral inflow, pulmonary venous flow, color M-mode and/or tissue Doppler (per European Society of Cardiology guidelines). * Experienced ≥ 1 of the following in last 12 months: Hospitalization for acute heart failure (primary diagnosis); Long term treatment with loop diuretic; Mean pulmonary capillary wedge pressure ≥ 16 mm Hg at catheterization for dyspnea; Left ventricular end diastolic pressure (LVEDP) ≥ 19 mm Hg at catheterization for dyspnea; Acute treatment with intravenous loop diuretic or hemofiltration. * On stable medical therapy in last 30 days before study entry (defined as no change in angiotensin converting enzyme inhibitors \[ACEI\], angiotensin receptor blockers, aldosterone inhibitors, beta-blockers or calcium channel blockers. * Satisfy these criteria at initial lab screening: Estimated glomerular filtration rate (eGFR) ≥ 30 ml/min; Corrected serum Ca 8.0-10.0 mg/dL (2.0-2.5 mmol/L); Phos ≤ 5.2 mg/dL (1.68 mmol/L); Serum albumin ≥ 3.0 g/dL (30 g/L); * Negative serum pregnancy test for females of childbearing potential (within 2 weeks of starting study treatment). * Women of childbearing potential must be practicing barrier/oral contraception during study-related treatment, or be surgically sterile or one year post-menopausal, be non-nursing and non-pregnant. Exclusion Criteria: * Taking \> 1,000 IU of vitamin D preparation daily within last 30 days. * Received activated vitamin D preparation including paricalcitol (Zemplar®), doxercalciferol (Hectorol®) or calcitriol (Rocalctrol®, Calcijex®) within last 90 days prior to study entry. * History of nephrolithiasis. * Poorly controlled hypertension (systolic blood pressure \> 180 mmHg and/or diastolic blood pressure \> 110 mmHg at Screening; confirmed by repeat). * Secondary hypertension (i.e. renal artery stenosis, primary aldosteronism or pheochromocytoma). * Severe hepatic impairment. * Use of known inhibitors (ie, ketoconazole) or inducers (ie, carbamazepine) of cytochrome P450 3A (CYP3A) within 2 weeks prior to taking study drug. * HIV positive. * Condition with prognosis \< 1 year at study entry other than heart failure. * Significant valvular disease defined as moderate or severe aortic or mitral stenosis, mitral or aortic regurgitation. * Infiltrative cardiac disease (sarcoid, amyloid, hemochromatosis, lymphoma, etc.). * Arrhythmogenic right ventricular cardiomyopathy. * Active myocarditis. * Constrictive or restrictive pericarditis. * Acute coronary artery disease symptoms defined as emergency department visit or hospital admission with unstable angina, ST-elevation myocardial infarction (STEMI), non-ST-elevation myocardial infarction (NSTEMI), percutaneous coronary intervention (PCI) or coronary artery bypass graft (CABG) within 90 days before study entry. * Poor echocardiographic windows. * Current active treatment in another investigational study or participation in another investigational study within 1 month before screening. * Active malignancies except in situ carcinoma of the cervix, localized squamous or basal cell carcinoma of skin. * Other serious concurrent or recent medical or psychiatric condition which, in Investigator's opinion, makes the patient unsuitable for participation.