This article develops a cost-effective and accurate measurement system for heart best intervals. The system is composed of an analog to digital (A/D) converter, an IBM personal computer (an 8088 microprocessor, an 8253-5 timer, an 8259A interrupt controller, and memories) and assembler programs for controlling these hardware components. An exponential smoothing algorithm effectively reduced noise effects from A/D converted electrocardiogram (ECG) signals influenced by 60 Hz alternating current (AC). The system can collect 15000 heart beat intervals with an 1/5400 second unit.