A system for measuring at least one of stroke volume and cardiac output from a patient, comprising: a current injection module comprising electrodes (24, 28) to be worn in the patient's clavicle/brachial region and an electrical circuit configured to inject a high-frequency, low amperage alternating current field along the course of the brachial artery in the clavicle/brachial region by means of the electrodes (24, 28); an impedance sensor connected to at least two of said electrodes (24, 28) to be attached to the patient in the clavicle/brachial region and comprising an impedance circuit, the impedance circuit configured to sense, simultaneously with the injection of the high-frequency, low amperage alternating current field, via the at least two electrodes (24, 28)and to signal process voltage changes produced within the current field to measure a transbrachial electro-velocimetry impedance signal from the patient; an optical sensor connected to an optical probe configured to be attached to the patient and comprising an optical circuit, the optical circuit configured to process signals from the optical probe to measure at least one optical signal from the patient; and a processing system configured to: i) be worn on the body; ii) operably connect to both the impedance sensor and the optical sensor; iii) receive the impedance signal from the impedance sensor and process it to determine a first value of at least one of stroke volume and cardiac output; iv) receive the optical signal from the optical sensor and process it to determine a second value of at least one of stroke volume and cardiac output; and v) collectively process both the first and second values of at least one of stroke volume and cardiac output to determine a third value of at least one of stroke volume and cardiac output. a current injection module comprising electrodes (24, 28) to be worn in the patient's clavicle/brachial region and an electrical circuit configured to inject a high-frequency, low amperage alternating current field along the course of the brachial artery in the clavicle/brachial region by means of the electrodes (24, 28); an impedance sensor connected to at least two of said electrodes (24, 28) to be attached to the patient in the clavicle/brachial region and comprising an impedance circuit, the impedance circuit configured to sense, simultaneously with the injection of the high-frequency, low amperage alternating current field, via the at least two electrodes (24, 28)and to signal process voltage changes produced within the current field to measure a transbrachial electro-velocimetry impedance signal from the patient; an optical sensor connected to an optical probe configured to be attached to the patient and comprising an optical circuit, the optical circuit configured to process signals from the optical probe to measure at least one optical signal from the patient; and a processing system configured to: i) be worn on the body; ii) operably connect to both the impedance sensor and the optical sensor; iii) receive the impedance signal from the impedance sensor and process it to determine a first value of at least one of stroke volume and cardiac output; iv) receive the optical signal from the optical sensor and process it to determine a second value of at least one of stroke volume and cardiac output; and v) collectively process both the first and second values of at least one of stroke volume and cardiac output to determine a third value of at least one of stroke volume and cardiac output.