The electrical activity of the heart can be monitored by an electrocardiogram. Electrodes are placed at different locations on the chest and each time the heart beats, there is a wave of electrical activity through the heart muscle. This test can detect very slight changes in the heart’s electrical activity through deflections on a monitor. An electrocardiogram can be used to detect and diagnose cardiac arrhythmias, which are abnormalities in the heart’s conduction system.