1. A pocket-sized, self-contained electrocardiogram monitor, comprising: (a) a pocket-sized housing having first and second sides; (b) a plurality of electrodes mounted on said second side of said housing; (c) circuit means contained within said housing for processing an electrocardiogram signal appearing upon said electrodes when said electrodes are placed in contact with a patient's chest, said circuit means including (1) means for selectively amplifying small signals near the baseline of said electrocardiogram signal without clipping said electrocardiogram signal; (2) A/D converter means for converting said electrocardiogram signal to a digital signal; and (3) digital processing means coupled to said A/D converter means for sampling said digital signal, selecting the maximum and minimum values in a set of at least four consecutive samples, and generating display drive signal values representative of said maximum and minimum values at a rate which is an integral fraction of the sampling rate; and (d) a dot-matrix, liquid-crystal display on said first side of said housing, said liquid-crystal display being coupled to said circuit means and responsive thereto to display said display drive signal values.