This paper presents the design of a programmable cardiac stimulator which is incorporated into a broader system of acquisition, processing and display of electrocardiographic signals. The stimulator was devised for use in arrhythmia surgery and electrophysiologic studies; it is implemented by means of two microprocessors, A and B, connected by an RS232 serial communication. Microprocessor A manages the user interface: console display, control function keys, data input and transmission of stimulation parameters. Microprocessor B processes the information received and implements the appropriate stimulation. Six available modes of stimulation are described as well as the parameters involved and the range of values that they cover. The auxiliary circuitry of microprocessor B is described in detail. It consists of four blocks: selection of the stimulation channel, conformation of the stimulation pulse, amplifier-differentiator sensing, and the subsystem for the study of the rheobase curve. Two general flowcharts and a description of the major routines are provided.