Post-operative thrombosis in vascular surgery results from either technical error of deficient arterial outflow and can be avoided by checking, during the operation, that the new circulatory conditions created are adequate. Among the most frequently used control methods arteriography occupies a prominent place but requires a sophisticated equipment to be truly reliable. Per-operative measurement of the blood flow is much simpler. It objectively assesses the haemodynamic value of the arterial reconstruction and provides useful information on the short-and medium-term patency of the vessels.