A system for determining a heart failure indicator indicative of a heart failure disease state in a biological subject, the system including: a) at least one signal generator coupled to first electrodes (323A, 323B) provided in electrical contact with the subject in use, the at least one signal generator being adapted to generate a drive signal; b) at least one sensor coupled to second electrodes (324A, 324B) provided in electrical contact with the subject in use, the at least one sensor being adapted to measure a response signal; and, c) at least one processing device that: i) at least in part controls the at least one signal generator and receives an indication of a measured response signal from the at least one sensor, allowing at least one impedance measurement to be performed across at least one body segment of the subject; ii) determines a first fluid level indicator using at least one first impedance value obtained by performing the at least one impedance measurement across at least a body segment of the subject at a first time; iii) determines a second fluid level indicator using at least one second impedance value obtained by performing at least one impedance measurement across at least a body segment of the subject at a second time; iv) determines a fluid level change using the first and second fluid level indicators; and, v) determines a heart failure indicator using the fluid level change, wherein the first and second fluid level indicators are a ratio of extracellular fluid levels in the body segment to total body water, and wherein the body segment includes at least a limb of the subject and a torso of the subject. a) at least one signal generator coupled to first electrodes (323A, 323B) provided in electrical contact with the subject in use, the at least one signal generator being adapted to generate a drive signal; b) at least one sensor coupled to second electrodes (324A, 324B) provided in electrical contact with the subject in use, the at least one sensor being adapted to measure a response signal; and, c) at least one processing device that: i) at least in part controls the at least one signal generator and receives an indication of a measured response signal from the at least one sensor, allowing at least one impedance measurement to be performed across at least one body segment of the subject; ii) determines a first fluid level indicator using at least one first impedance value obtained by performing the at least one impedance measurement across at least a body segment of the subject at a first time; iii) determines a second fluid level indicator using at least one second impedance value obtained by performing at least one impedance measurement across at least a body segment of the subject at a second time; iv) determines a fluid level change using the first and second fluid level indicators; and, v) determines a heart failure indicator using the fluid level change, wherein the first and second fluid level indicators are a ratio of extracellular fluid levels in the body segment to total body water, and wherein the body segment includes at least a limb of the subject and a torso of the subject. i) at least in part controls the at least one signal generator and receives an indication of a measured response signal from the at least one sensor, allowing at least one impedance measurement to be performed across at least one body segment of the subject; ii) determines a first fluid level indicator using at least one first impedance value obtained by performing the at least one impedance measurement across at least a body segment of the subject at a first time; iii) determines a second fluid level indicator using at least one second impedance value obtained by performing at least one impedance measurement across at least a body segment of the subject at a second time; iv) determines a fluid level change using the first and second fluid level indicators; and, v) determines a heart failure indicator using the fluid level change, wherein the first and second fluid level indicators are a ratio of extracellular fluid levels in the body segment to total body water, and wherein the body segment includes at least a limb of the subject and a torso of the subject.