Embodiments of the present disclosure relate to a system and method for non-invasively determining a cardiac output of a patient that may include a photoacoustic sensor and a determination of oxygen uptake of the patient. Specifically, a signal from a photoacoustic sensor may be used to determine a mixed venous and an arterial oxygen saturation of the patient. The parameters of mixed venous and arterial oxygen saturation in conjunction with oxygen uptake may be used to calculate cardiac output using the Fick method.
