FLEX Vessel Prep Prior to Angioplasty in Native Arteriovenous Fistulae (AVF)

Inclusion Criteria: 1. Patient is ≥21 years of age. 2. Patient has a life expectancy of ≥12 months. 3. Patient has a native AV fistula created ≥ 60 days prior to the index procedure. 4. The target AV fistula has undergone successful dialysis for at least 8 of 12 sessions during a four-week period. 5. Patient has a de novo and/or non-stented restenotic lesion located between approximately 2 cm proximal to the arteriovenous anastomosis and axillosubclavian junction with ≥50% stenosis. 6. Patient has a target lesion (which may include a tandem lesion) that is ≤ 100 mm in length (by visual estimate). Note: Tandem lesions may be enrolled provided they meet all of the following criteria: * Separated by a gap of ≤ 30mm (3 cm). * Total combined lesion length, including 30 mm gap, ≤ 100 mm. * Able to be treated as a single lesion. 7. Patient has a target vessel diameter of 4.0 - 12.0 mm (by visual estimate) 8. Patient underwent successful crossing of the target lesion with the guidewire. 9. Patient provides written informed consent prior to enrollment in the study. 10. Patient is willing to comply with all follow-up evaluations at specified times. Exclusion Criteria: 1. Patient is pregnant or breastfeeding. 2. Patient is receiving immunosuppressive therapy. 3. Patient has undergone prior intervention of access site within 30 days of index procedure. 4. Patient with anticipated conversion to peritoneal dialysis. 5. Patient has an infected AV access or systemic infection. 6. Patient has planned surgical revision of access site. 7. Patient with secondary non-target lesion requiring treatment within 30 days post index procedure. 8. Patient with hemodynamically significant central venous stenoses that cannot be successfully treated prior to treatment of the target lesion. 9. Patient with target AVF or access circuit which previously had thrombectomy within last 30 days. 10. Patients judged to have a lesion that prevents complete inflation of an angioplasty balloon or proper placement of the delivery system. 11. Patient with target lesion located central to the axillosubclavian junction. 12. Patient has significant arterial inflow lesion requiring treatment more than 2 cm upstream from the anastomosis in the AV access. 13. Patient has presence of pseudoaneurysm or aneurysm requiring surgical revision at the target lesion site. 14. Patient with known contraindication, including allergic reaction, or sensitivity to contrast material that cannot be adequately pre-treated. 15. Patient who cannot receive recommended antiplatelet and/or anticoagulant therapy. 16. Patient with clinically significant Steal Syndrome requiring treatment. 17. Patient is enrolled in another investigational drug, device, or biologic study and has not completed the primary endpoint or was previously enrolled in this study. 18. Patient has a co-morbid condition that, in the judgment of the Investigator, may cause him/her to be non-compliant with the protocol or confound the data interpretation. 19. Patient has AV fistula created via endovascular technique.