Electro cardiography (ECG) monitoring is an important method for cardiac disease detection and prevention. With the development of telemedicine, ECG real-time monitoring becomes more convenient. The rise and popularization of smartphone provide a new technical means for ECG monitoring. This paper focuses on the development of software for an ECG monitoring system on a smartphone platform. The system includes a client and a center. The client is developed on smartphone. Its main function is process and diagnose ECG signal. A wavelet method is used to detect the QRS-complex and diagnostic criteria are formulated to diagnose 14 kinds of arrhythmia disease. The tele-monitoring center is developed on a PC with LabVIEW, which receives ECG signal and diagnosis from smartphone by GPRS. Results show that the system can monitor ECG and diagnose arrhythmia by calculating the heart rate in real time. The proposed system is reliable and gives good real-time performance.