A biomedical apparatus for pumping blood of a human or an animal patient through a secondary intra- or extracorporeal blood circuit (10, 11, 12), comprising a blood pump for pumping blood, an inlet duct connected to the blood pump, for being inserted into a patient's circulatory system, in order to guide blood of the patient to the blood pump, an outlet duct connected to the blood pump, for being inserted into the patient's circulatory system, in order to guide blood from the blood pump back to the patient's circulatory system, a measuring device for measuring at least one physical parameter of the heart or of a blood vessel of the patient, the measuring device being adapted to be arranged inside the heart or the blood vessel, and a controller for regulating the power of the blood pump based on the measured physical parameter, wherein the controller is configured to determine an estimate for an end-diastolic inner volume of the heart based on the physical parameter and is configured to regulate the power of the blood pump depending on this estimate, characterized in that the measuring device is adapted to send out an electromagnetical or a mechanical wave and the controller is configured to regulate the power of the blood pump based on the following linear function: PW des t = EDV t − EDV 0 ⋅ k prsw, in which PW des (t) denotes the desired pump work per heartbeat at a certain time t and EDV(t) an estimate for the end-diastolic volume of the heart determined based on the measured physical parameter, and in which the two parameters EDV 0 and k prsw denote the end-diastolic volume at which the desired pump work is zero and the gain of the pump work relative to the estimated EDV(t), respectively. a blood pump for pumping blood, an inlet duct connected to the blood pump, for being inserted into a patient's circulatory system, in order to guide blood of the patient to the blood pump, an outlet duct connected to the blood pump, for being inserted into the patient's circulatory system, in order to guide blood from the blood pump back to the patient's circulatory system, a measuring device for measuring at least one physical parameter of the heart or of a blood vessel of the patient, the measuring device being adapted to be arranged inside the heart or the blood vessel, and a controller for regulating the power of the blood pump based on the measured physical parameter, wherein the controller is configured to determine an estimate for an end-diastolic inner volume of the heart based on the physical parameter and is configured to regulate the power of the blood pump depending on this estimate, characterized in that the measuring device is adapted to send out an electromagnetical or a mechanical wave and the controller is configured to regulate the power of the blood pump based on the following linear function: PW des t = EDV t − EDV 0 ⋅ k prsw, in which PW des (t) denotes the desired pump work per heartbeat at a certain time t and EDV(t) an estimate for the end-diastolic volume of the heart determined based on the measured physical parameter, and in which the two parameters EDV 0 and k prsw denote the end-diastolic volume at which the desired pump work is zero and the gain of the pump work relative to the estimated EDV(t), respectively.