Harvard Heart Letter

Electrocardiogram: Visualizing the heart's electrical signature

A recording of the heart's electrical activity offers clues to its health and problems.

Editors' note: We are often asked about various tests used to check the heart and blood vessels. With this article we begin an occasional series describing the diagnostic tests that readers are likely to encounter.

In 1887, British physiologist Augustus Desiré Waller used a device containing mercury and sulfur placed on the skin of the chest to record the heart's electrical activity. More than a century later, the descendants of that contraption provide one of the most commonly used tests for heart disease — the electrocardiogram. The squiggle of lines it records yields valuable information about the health of the heart or problems in and around it.

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