The present invention addresses the problem of providing a system for monitoring the heart condition a target fish in a state equivalent to a natural state. This problem is solved by a system for monitoring the heart condition of fish that is provided with a container and a processing device, wherein the container includes a plurality of detectors on the inner wall surface of the container and a space in which fish can swim on the side opposite to the detector side, with respect to the fish in the container, and the processing device includes an acquisition unit that acquires, in a time series, photoelectric pulse waves of a plurality of parts of the fish over a predetermined detection period under signal synchronization through a measurement device having the plurality of detectors, and an extracting unit that extracts a portion that most reflects the photoelectric pulse wave of the heart part of the fish from the photoelectric pulse waves of the plurality of parts acquired during the detection period.
