ECG ST segment should be monitored for myocardial ischemia diagnosis. But this information needs a very accurate ECG acquisition. This paper presents the design of a chopper amplifier filtering the baseline wander and minimizing the added electronic noise with an acceptable ST segment distortion. A method is proposed to estimate the ST segment distortion and compare it to the International Electrotechnical Commission (IEC) standards. The design is achieved using XFAB 180nm technology and validated at transistor-level simulation for typical and worst cases.