A low-cost system for digital transmission of the electrocardiogram (ECG) from a remote location to a medical facility under emergency conditions is developed. Delta threshold, Aztec and a hybrid combination of these two data compression techniques are evaluated to determine their ability to accomplish real time transmission of the ECG over a telephone system. The evaluations are performed using ten electrocardiograms representing arrhythmias commonly encountered in the emergency setting. It is shown that the delta threshold technique may cause data expansion under certain conditions. The hybrid technique is the optimum choice and real-time transmission can be accomplished over a 2400 BAUD system.