Patients with stage IV and V chronic kidney disease and end stage renal disease requiring hemodialysis at University of Alabama at Birmingham (UAB) Dialysis Clinics will be recruited from the UAB Vascular Access Clinic, which has been the site for recruitment of patients requiring new vascular access for the last 10 years.

The main purpose of this research study is to conduct a research study to determine if Sildenafil compared to placebo will improve the vascular health of arteries and veins before arteriovenous fistula creation (shunt) and how quickly your veins and arteries dilate and increase in blood flow after fistula creation. An arteriovenous fistula (shunt) is a connection between the artery and vein in the arm for dialysis use. Another purpose of this study is to determine if Sildenafil reduces the blood and tissue levels of oxidants prior to fistula creation. Oxidants are harmful substances in the body that damage the cells tissues, and organs.

Inclusion Criteria:

1. Age ≥19 years of age male or female
2. Chronic Kidney Disease Stage IV or V patients or End Stage Renal Disease Patient requiring arteriovenous fistula surgery

Exclusion Criteria:

1. Patient currently on nitrate therapy or any nitric oxide donor in any form
2. Patient currently on protease inhibitor or non-nucleoside reverse transcriptase inhibitor
3. Patient with resting systolic blood pressure <90 mm Hg and diastolic blood pressure < 50 mm Hg.
4. Patient life expectancy < nine months.
5. Patient unable or unwilling to meet study requirements.