Embodiments include a method of determining an oxygen content in a bodily tissue or in blood of a human or animal body, wherein a variable representative of oxygen content in the bodily tissue or in the blood is detected at least over one cardiac cycle and is correlated with a contraction state of a heart. Embodiments include a device configured to be inserted into the human or animal body, wherein the device includes at least one sensor unit that detects a signal representative of an oxygen content along a measurement path. Embodiments include a reflector provided on the device, wherein the reflector is arranged in the measurement path between a transmitter and a receiver of the at least one sensor unit to reflect the signal.