Because of the low-cost and large availability of personal computers as well as their highly increasing performance and reliability, PC’s have been employed in many fields of science. The most common one of these fields are the biomedical instruments. Electrocardiograph or shortly named “ECG” is one of the oldest instrument-bound measurements in medicine. It has faithfully followed the progression of instrumentation technology. ECG machine is used to record the electrical activity generated by the heart in order to be diagnosed by the doctor.The overall objective of this project is to design and implement a prototype of a PC-based 12-lead ECG system. The system consists of the implemented hardware boards and any PC which satisfies the system requirements, interfaced with each other using the printer cable connected to the LPT printer port. The designed system has a suitable size and can be moved and installed easily, besides that a Windows-based program designed using Microsoft Visual C++.NET with a Graphical User Interface (GUI) has been developed and installed on the PC so that it can be used easily by the operator. The program has the capability of drawing 6-lead traces at a time as well as printing them on a paper using any traditional printer available.The implemented system has been tested and operated successfully and many practical ECG traces have been obtained from different cases to ensue the reliability and accuracy of the implemented system.