An apparatus for recording the movements of the heart and great vessels or of the diaphragm on a single film.

It consists of a lead sheet called the grid in which are cut horizontal or vertical slits, typically less than 1 mm wide, spaced 1-2 cm apart.

During an X-ray exposure lasting as long as several cardiac or respiratory cycles, the grid or the film is moved vertically to record cardiac motion or horizontally for diaphragm motion.