Principle of <a href="https://en.wikipedia.org/wiki/Electrocardiography" class="extiw" title="en:Electrocardiography">ECG</a> formation, fast
<a href="//commons.wikimedia.org/wiki/User:Kalumet" title="User:Kalumet">Kalumet</a>
CC BY-SA 3.0
selbst erstellt = <span class="int-own-work" lang="en">Own work</span>