Summary. In 1903 Willem Einthoven published in Pflügers Arch his classic article on the investigation of human electrocar- diogram by his string galvanometer. Many historians of medicine, Einthoven also marked that publication as the beginning of clinical electrocardiography. Many investigators like Galvani, Manteucci, Kölliker, Müller, Lipmann, Waller, Ader, Einthoven, Lewis, Wilson and others participated in creation and development of electrocardiogram. From that time electrocardiogram quickly became, and has remained the most essential diagnostic laboratory tool in investigation of heart diseases. The aim of this article is to remined us of the beginning of this part of cardiology 100 years ago.