Using non-linear dynamics methods, we have comparatively analyzed the HRV (heart rate variability ) of the healthy people and the HRV of those with arrhythmia. The Lyapunov exponent of the healthy group\'s HRV is different from that of the arrhythmia group\'s HRV. The largest Lyapunov exponent of the healthy people\'s HRV is 0.45907. But in the abnormal situation, the value of a reduces, and the largest Lyapunov exponent of the arrhythmia group\'s HRV is 0. 41472. They are both chaotic system, however the level of the chaos of those with arrhythmia is apparently lower than that of the healthy people.