In this study, a portable ECG device is introduced to monitor the patient's electrocardiogram (ECG). Electronic hardware consists of Raspbery Pi, preamplifier, low-pass and high pass filters, gain unit, DC level shifter and analog-digital converter circuits. ECG signal is obtained by the electrodes which attached to the skin surface is amplified by the INA128P operational amplifier. Then, the signal is filtered, amplified and added DC offset, respectively. MCP3208 is used to convert the result signal from analog to digital. By this way, ECG signal is converted to 12-bit digital signal and sent to the GPIO port of the Raspberry Pi. ECG signal is shown at the portable device's screen via a developed software using the Python language.