We enroll 60 patients with stable congestive heart failure (CHF) based on the following criteria: Inclusion Criteria: 1- ambulatory New York Heart Association (NYHA) class ≤ III, 2- LVEF ≤ 45%, 3- Stability for at least 3 months (no exacerbation, no change in medication) and exclusion Criteria: 1- Therapy with steroids or anticonvulsants and vitamin D supplements, 2- Prior history or present hypercalcemia (serum calcium≥10.5mg/dl), 3- History of renal stone, 4- Persistent atrial fibrillation (to optimize the reproducibility of our estimation of LV function). After obtaining written consent, Patients will be randomly divided in 2 groups of interventions and controls, and then will be asked to take visually identical capsules per week of either placebo or vitamin D. Intervention group will receive 50000 IU vitamin D per week for 6 months, and controls will receive exactly similar placebo (cellulose) capsules regarding shape, size and taste as cases. Treatment will be conducted for a period of 6 months. Both groups will receive a daily supplement of 500 mg oral calcium. At the base line visit and at the end of study we will perform transthoracic echocardiography to evaluate LVEF and blood sample of each subject will be taken for Ca++, p, Alb, 25(OH) D, Cr. Patients will be reviewed every month. NYHA status at the end of the study will be evaluated again.