Context: In this project we aimed to investigate the ECG-measurement which is used to monitoring the heart activity in order to discover heart problems based on the beats and rhythms. Therefore this old technology is very popular at clinics.

Objective: The purpose of this research was to find out how it is possible to maximize the accuracy of ECG-measurement by applying a differential amplifier. In fact there is a vast area to do research for this topic since it is related to human`s health improvement and will never be old or out of value.

Methods: We started our work with literature review from relevant references in order to gather information about Electrocardiography, ECG, and how the function of the human heart results in electrical signals Later on we performed an experiment which was done in BTH. In the experiment we created an ECG measurement circuit, containing two OP-amplifier circuits connected as a differential amplifier with high gain.. This circuit was connected to a human body with special electrodes and the output connected to an oscilloscope. In order to record heart activity, electrodes coming from different parts of the body including the chest, wrists and ankles were connected to the inputs of the ECG measurement circuit. The signals obtained from the body are very weak to register, therefore a differential amplifier is appropriate to amplify them, and to reduce interference and noise. In our case the amplification of the ECG measurement circuit was calculated to be around 120 times, which was enough to give clear pictures on the oscilloscope.

Results: Finally we could see the results of the ECG- measurement on the oscilloscope monitor which was corresponding to our heartbeats. It was easily visible that how amplifiers can effect on the measurement by comparing the results before and after reduction of interference and noise. Very important here was how well the circuit was grounded. If the circuit was grounded in a good way, this resulted in less interference and noise.

Keywords: Theory for ECG, ECG-history, ECG-measurement; differential amplifier;