A computer system has been developed to measure the electrical activation sequence of the heart during ventricular tachyarrhythmias. The system incorporates 32 channels of parallel analog-to-digital conversion, rapid generation of results, a high degree of user interaction, and ability to capture events occurring at essentially random times. The system has been used extensively in the animal laboratory as a prototype for a system to be used in the surgical treatment of ventricular tachycardia. It has been shown to be an effective and practical tool in the location of the site of early activation during cardiac arrhythmias. © 1980.