Aim — the objective of the study was to determine in the ex vivo experiment the parameters of energy effects during the radiofrequency vein ablation procedure with the use of the Closure Fast electrode necessary for the complete denaturation of the venous wall collagen. Material and methods. A total of 27 samples of great saphenous veins were taken during phlebectomy. Segmental heating of the  venous wall was carried out using a standard VNUS machine. The digital images of the temperature field were obtained by means of  non-contact thermography. The fraction of intact collagen in the samples was determined by differential scanning calorimetry. The degree of collagen denaturation was calculated from the decrease of the thermal denaturation effect. The contraction of the tissue served as an additional indicator of collagen denaturation. Results. In the first cycle the heating temperature increased constantly and reached 85±5 °C. In the second cycle the temperature reached a plateau 91±2 °C within 10 seconds. It was shown that a single cycle of segmental heating proved insufficient to completely destroy the collagen skeleton of the tissue, the degree of denaturation at the center of the segment being 73±12%. Two standard cycles were sufficient for collagen denaturation in the middle portion of the vein; as a rule the skeleton was destroyed even though the process of collagen denaturation was not completed at the edges of the segment. The remaining macromolecules totally disappeared after three cycles of exposure. Conclusion. A single standard cycle of segmental heating of the venous wall using the  Closure Fast electrode does not lead to complete degradation of the collagen tissue. Two standard cycles are usually sufficient to achieve amorphization of the venous matrix and tissue shrinkage.