When was first ECG machine invented?

in the 20th century

The Heart's beat is caused by voltage changes in it's muscle fibres. The changes can be detected by a voltmeter. This electrical activity was first recorded by the Dutch physiologist William Einthoven in 1903 at Leyden University using a primitive galvanometer.

To this day, the Electrocardiogram remains basically the same, despite many modifications.

1903 is when Einthoven invented the first Electrocardiograph!!