Hundred years ago, in 1907, A. Keith and M. Flack described histologically in the right atrium of different mammalian including human hearts a structure which they called sinu-auricular node and which they interpreted as the place where the heart beat originates. One year earlier K.F. Wenckebach had reported on an arrhythmia which he explained by polygraphic technique as "vein-atrial block" (today: sinoatrial block). To such an assumption he had to suppose that the heart action begins in the vena cava superior where he described a "small but interesting musculature" above the atrium as the morphological basis of the origin. Recently, with regard to the publication dates of these findings it was claimed (W. Ehrlich) that we should owe the honour of having discovered the sinus node morphologically to Wenckebach and not to Keith and Flack. Referring to the original publications it is shown that Wenckebach as well as Keith and Flack refered to different ideas. Wenckebach supposed the location of the origin of the heart beat in a macroscopically discernible muscle placed at the vena cava superior just above but separated from the right atrium. As the only connection capable of conduction between both he described a special bundle. On the contrary, Keith and Flack depicted as the place where the heart action begins a microscopically defined structur in the atrium at the junction of the vena cava superior with the sorrounding venous and atrial musculature being not separated from each other. Scientific progress corroborated the interpretation of Keith and Flack, while Wenckebach desisted only slowly from his position which, after all, proved incorrect.