Device for determining the blood volume and/or blood volumetric flow of a circulation section, with - a fluid storage unit (2) for storing a measuring fluid (3), - an injection means, especially a catheter (11) or a cannula, for injecting the measuring fluid (3) into the circulatory system, - at least one pump device (5). arranged between the fluid storage unit (2) and the injection means, - means for determining at least one property of the measuring fluid (3) prior to the injection into the circulatory system, - means for determining the respective property in the circulatory system downstream from the injection site, and - an analysis device for calculating the blood volume or volumetric flow as a function of the properties determined, characterized in that the measuring fluid (3) can be taken from the fluid storage unit (2) by means of a first pump device (5) to a second pump device (9) and from the second pump device (9) to the blood circulation.
