The heart-shadow section display system displays the correct contours of the heart using binary quantised picture signals as video signals. Centre line pulses are applied to the sitting input of a flip-flop (16) and the contour signal (17) to its reset input. The flip-flop output is passed to a pulse shaper (20) that produces a pulse from one edge. This pulse is delayed (21) by one line and returned to the flip-flop other reset input as a limiting pulse. The delay circuit is controlled by a regulator (24) whose control voltage is derived from a time comparison of the flip-flop output, the contour signal (17) and the limiting pulse (22).