a. Heart Electrical Forces. During the cardiac cycle (one contraction of the heart plus the relaxation period that follows), electrical changes take place in the heart.

These changes can be visualized and recorded.

(1) Detection of electrical forces in the heart. Electrical forces in the heart can be detected on the body’s surface. Therefore, electrodes attached to the patient’s skin can detect electrical forces in the heart.

(2) Recording of electrical forces in the heart. The recording of the electrical changes during the cardiac cycle is called an electrocardiogram (ECG or EKG). The instrument used to record these changes is an electrocardiograph.