The significant of giving immediate therapy to person who has heart attack leads to inventing automatic equipment or device being able to provide therapy when doctors or trained people cannot reach the patient in time. Ventricular tachycardia (VT) and ventricular fibrillation (VF) are two major arrhythmias causing sudden cardiac death. Arrhythmia classifier functions to detect arrhythmias and classifies VT and VF via electrocardiogram (ECG). Once VT is detected, a pattern of small electric pacing is given to lead pumping of heart back to normal. While VF needs defibrillation by giving electric shock to terminate.

The first generation of arrhythmia detector uses heart rate to detect arrhythmias by the property that VT and VF have faster rate than normal heart rhythm (Sinus rhythm, SR). Detecting by rate can be misinterpreted when patient is in exercise or running and applying shock when patient does not need it causes pain and discomfort. Therefore, an accurate diagnosis is required to reduce pain and discomfort.

Kalman filter is used in study behaviors of arrhythmias and sinus rhythm in order to find unique characteristic of VT, VF, and SR in a set of patients. With these results, classification criteria will be defined.