Objective The mechanism about biofeedback is not complete clear. Our aim was to study changes of cardiac function (electrophysiology) during biofeedback with the help of approximate entropy (ApEn), and a potential new mechanism about neurofeedback may be detected. Methods A total of 30 healthy volunteers participated in this study which consisted of the neurofeedback group(n=20) and the control group (n=10). We applied electromyogram neurofeedback as the feedback method, and simultaneously recorded electroencephalogram(EEG) and electrocardiogram(ECG). We applied the nonlinear analysis ApEn assess obtained data. Results In the biofeedback group the average of heart rate was higher than that of control group in the last two sessions. As the biofeedback experiment sessions were progressed, the standard deviation of heart rate gradually reduced and the ApEn of ECG increased with statistic significance in the biofeedback group. Conclusion We found that biofeedback can influence cardiac electrophysiological system and make cardiac systems progress healthily and achieve greater ability of anti-stress.