A percutaneous blood pump system (100, 1400) comprising: a blood pump (100, 1402) configured to be positioned in a heart, the blood pump comprising: a cannula; a sensor (112, 1407) configured to measure an aortic pressure in the heart; and a motor (108, 1405) operable at a motor speed and configured to draw a variable motor current to provide a level of cardiac support to the heart; a controller configured to control the motor current and motor speed, the controller comprising: a memory; a user interface (300, 500); and a processor configured to: measure the motor current and the motor speed of the motor; receive an indication of the aortic pressure from the sensor and convert the indication of the aortic pressure to an aortic pressure measurement; determine a pressure gradient across the cannula associated with the motor current and the motor speed; calculate at least one cardiac parameter based on the aortic pressure measurement and the pressure gradient across the cannula; record the at least one calculated cardiac parameter in the memory; calculate, based on the at least one cardiac parameter, one or more heart function parameters; determine, based on at least one of the at least one cardiac parameter and the one or more heart function parameters, a recommended change to the level of cardiac support to the heart; and, characterised in that the processor is further configured to generate for display on the user interface the recommended change to the level of cardiac support. a blood pump (100, 1402) configured to be positioned in a heart, the blood pump comprising: a cannula; a sensor (112, 1407) configured to measure an aortic pressure in the heart; and a motor (108, 1405) operable at a motor speed and configured to draw a variable motor current to provide a level of cardiac support to the heart; a controller configured to control the motor current and motor speed, the controller comprising: a memory; a user interface (300, 500); and a processor configured to: measure the motor current and the motor speed of the motor; receive an indication of the aortic pressure from the sensor and convert the indication of the aortic pressure to an aortic pressure measurement; determine a pressure gradient across the cannula associated with the motor current and the motor speed; calculate at least one cardiac parameter based on the aortic pressure measurement and the pressure gradient across the cannula; a cannula; a sensor (112, 1407) configured to measure an aortic pressure in the heart; and a motor (108, 1405) operable at a motor speed and configured to draw a variable motor current to provide a level of cardiac support to the heart; a controller configured to control the motor current and motor speed, the controller comprising: a memory; a user interface (300, 500); and a processor configured to: measure the motor current and the motor speed of the motor; receive an indication of the aortic pressure from the sensor and convert the indication of the aortic pressure to an aortic pressure measurement; determine a pressure gradient across the cannula associated with the motor current and the motor speed; calculate at least one cardiac parameter based on the aortic pressure measurement and the pressure gradient across the cannula; a memory; a user interface (300, 500); and a processor configured to: measure the motor current and the motor speed of the motor; receive an indication of the aortic pressure from the sensor and convert the indication of the aortic pressure to an aortic pressure measurement; determine a pressure gradient across the cannula associated with the motor current and the motor speed; calculate at least one cardiac parameter based on the aortic pressure measurement measure the motor current and the motor speed of the motor; receive an indication of the aortic pressure from the sensor and convert the indication of the aortic pressure to an aortic pressure measurement; determine a pressure gradient across the cannula associated with the motor current and the motor speed; calculate at least one cardiac parameter based on the aortic pressure measurement and the pressure gradient across the cannula; record the at least one calculated cardiac parameter in the memory; calculate, based on the at least one cardiac parameter, one or more heart function parameters; determine, based on at least one of the at least one cardiac parameter and the one or more heart function parameters, a recommended change to the level of cardiac support to the heart; and, characterised in that the processor is further configured to generate for display on the user interface the recommended change to the level of cardiac support.