[Willem Einthoven. Thoughts on the occasion of his 125th anniversary]

125 years ago William Einthoven (May 21st, 1860, to Sept. 28th, 1927) was born. Already at the age of 25 he was appointed professor for physiology at Leiden University, Holland. From 1894 to 1913 he worked out essential fundaments of modern electrocardiology. He constructed the string galvanometer and thus he created an essential technical basis for the development of clinically applicable electrocardiographs. Apart from the electrocardiography also the phonocardiography owes decisive impulse to Einthoven and his school. Besides a biographical outline the paper gives a survey of essential facts of our electrocardiographic knowledge going back to Einthoven and compiles the most important papers in a selective bibliography.