A portable instrument for monitoring body electrocardiogram (ECG) was introduced, and the extraction of Heart Rate Variability (HRV) signals from ECG was achieved by picking up R peaks of ECG with wavelet transform technique. The nonlinear parameters (correlative dimensions, maximum Lyapunov exponents) of the HRV signals extracted from normal and arrhythmia ECG signals were calculated, and the results showed that the nonlinear parameters calculated from the HRV signals were helpful for analyzing human's health state and diagnosing of heart diseases.