On the diagram of the ECG, the letter ________, or P wave, indicates that an electrical impulse was sent through the atria.

ECG

Electrocardiogram, a non-invasive test that records the electrical activity of the heart to assess its health and detect any abnormalities.

P Wave

The first wave in an electrocardiogram, representing the depolarization of the atria of the heart.

Electrical Impulse

A sudden surge of electrical energy or power, typically referring to the signals transmitted within biological organisms, especially neurons.