The discoveries by Galvani and Volta of electricity and its effects fascinated the intellectual world, but it was not until 1856 that Köllicker and Müller discovered that the heart muscle could produce electric activity. Muirhead in London recorded the first electrocardiogram (ECG) in man in 1869 or 1870 with a siphon instrument and Waller in 1887 with a capillary electrometer. Einthoven's string galvanometer was a breakthrough. As early as five years after his publication Einthoven introduced "Le Télecardiograme" in 1906 by which a cable connected his instrument to a hospital one and a half kilometres away. The string galvanometer produced precise ECG recordings but it was like the opera primadonnas of the time, voluminous and unpredictable. Rune Elmqvist developed the direct-writing inkjet recorder, first demonstrated at the Congress of Cardiology in Paris, 1950. Ohnell's studies of preexcitation, to which the WPW-syndrome belongs, were important. After the initial focus on arrhythmias, ECG became more and more used in the diagnosis of myocardial ischaemia and coronary heart disease. To refine this diagnosis the hypoxaemia (breathing air with low oxygen content) test, as well as the exercise test and other stress tests were introduced. Vectorcardiography displays the spatial movements of the electrical forces generated by the heart. Long-term ECG registration with a portable tape recorder is important both for the diagnosis of arrhythmias and myocardial ischaemia. Foetal and comparative ECG have provided important clinical and scientific information.