When designing an Electrocardiograph (ECG), its efficiency and the acquisition of a clean and diagnosable ECG signal depends upon the accurate selection and combination of electronic components as well as the techniques used for noise elimination. This book goes through the design and development of a Single Chanel 3-Lead Electrocardiograph and a Software-based processing environment. Main design characteristics include: Reduction of common mode voltages, good protection for the patient, use of the ECG device for both monitoring and automatic extraction and measurements of the ECG components by the software. An efficient ECG hardware has been developed which lowers the influence of common mode voltages and consists of a lead selection stage so that the user is able to select which bipolar lead to record, a pre-amplification stage for amplifying the differential potentials while rejecting common mode voltages, an electrical isolation stage from three filtering stages with different bandwidths for noise attenuation, a power line interference reduction stage and a final amplification stage