Although in-situ monitoring of electrical resistance of polymer-supported thin films during a mechanical test is frequently used, the impact of the magnitude of electric current on material behavior in such experiments remained unknown. Here, we report on cyclic straining of polymer-supported gold metallization lines under direct current of different magnitudes. Fatigue damage in form of localized extrusions becomes more pronounced with increasing current as a result of Joule heat and material softening. After a critical current value is reached, crack propagation results in a local decrease of line cross-section leading to thermal runaway and open circuit failure.