A self-powered wearable electrocardiography (ECG) system is demonstrated. The ECG sensing circuit was fabricated on a flexible PCB and powered by a wearable thermoelectric generator (w-TEG) using body heat as the energy source. To allow the TEG to obtain a large temperature difference for high power generation and also be wearable, a polymer-based flexible heat sink (PHS) comprised of a superabsorbent polymer (SAP) and a fiber that promotes liquid evaporation was devised. Parametric studies on the PHS were conducted, and the structure of the w-TEG was also optimized for the PHS. The output power density from the w-TEG with the PHS was over 38 mu W/cm(2) for the first 10 min and over 13 mu W/cm(2) even after 22 consecutive hours of driving the circuits. This power level is high enough to continuously drive the wearable ECG system, including the sensors and the power management circuits.