Public domain photos

The image shows an old book with a graph on it, which is an electrocardiogram. The graph is composed of a series of lines that represent the electrical activity of the heart, and the text on the paper provides further information about the graph.

The image shows an old book with a graph on it, which is an electrocardiogram. The graph is composed of a series of lines that represent the electrical activity of the heart, and the text on the paper provides further information about the graph.Open in library