Patients will undergo at baseline and regular intervals:

• clinically indicated bloodwork/urine and echocardiogram testing
• biomarker studies

Upon enrolment in the study patients will be divided into 4 groups normal, mildly deficient and severely deficient. Normal and mild vitamin D levels will receive no treatment while severe Vitamin D deficiency will be randomized (50/50) to receive no treatment or vitamin D treatment. They will be seen in the heart failure clinic every 6 months. The patients will be followed for 26 months.

The inclusion criteria for the study is:

• an EF ≤40% within the last 12 months before recruitment
• established diagnosis of heart failure
• >18 years of age
• patients will vitamin d levels of sufficient, mild deficiency and severe deficiency

The exclusion criteria is:

• hypercalcemia
• known hypersensitivity to Vitamin D
• patient unwilling to comply with study requirements
• any other disease other than heart failure that can alter the patients quality of life over a period of 6 months
• women of child bearing potential
• a patient currently taking vitamin d
• severe renal impairment estimated glomerular filtration rate (eGFR) <30

Inclusion Criteria:

• an ejection fraction (EF) ≤40% within the last 12 months before recruitment
• established diagnosis of heart failure
• >18 years of age
• patients with Vitamin D levels of sufficient, mild deficiency and severe deficiency

Exclusion Criteria:

• hypercalcemia
• known hypersensitivity to Vitamin D
• patient unwilling to comply with study requirements
• any other disease other than heart failure that can alter the patients quality of life over a period of 6 months
• women of child bearing potential
• a patient currently taking vitamin d
• severe renal impairment eGFR <30