The invention relates to a system for determining blood flow within a blood vessel (18). A fluid infusion unit (4, 10, 11) continuously infuses a fluid into the blood vessel, and a temperature values determining unit (14, 21) determines simultaneously a first temperature value at a first location and a second temperature value at a second location such that the first temperature value is indicative of the temperature of the fluid and the second temperature value is indicative of the temperature of a mixture of the fluid and the blood. The blood flow is determined based on the measured first and second temperature values and the infusion rate. This kind of determining the blood flow leads to an increased accuracy and is less cumbersome than known techniques requiring a movement of a temperature sensor for measuring temperatures at different locations.
