In total 56 eligible patients will be enrolled after giving informed consent. Screening will take place in the preceding 6 weeks before scheduled AVF creation. Only patients receiving a Brescia - Cimino (radio - cephalic) fistula or a distal ulnar artery to basilica vein, proximal radial artery to transposed basilica vein, brachial artery to transposed basilica vein and brachial artery to cephalic vein will later be randomized. Patients will be randomly assigned in equal proportions (each group 28 patients) to receive either topically applied heparin (Heparin 2,400 IU /ml Cutaneous Spray) or placebo using a computer-generated randomization. Participants and members of the study team will be blinded to treatment assignment. Patients will be instructed how to use and administer study medication for the consecutive 24 weeks following randomization.