Final answer:
An electrocardiogram (ECG or EKG) is a diagnostic tool that records the voltages created by heart depolarization and repolarization to assess the electrical activity and functionality of the heart muscle.
Step-by-step explanation:
A test that records the electrical activity of the heart is known as a(n) electrocardiogram (ECG or EKG). An ECG is a record of the voltages created by the wave of depolarization and subsequent repolarization within the heart. These electrical impulses are vital for the heart to function properly, as they regulate the heartbeat. Electrodes are placed on the chest (and sometimes limbs) to measure voltages between pairs, which are then graphed to provide an indication of heart muscle function. The most commonly used graph is the lead II potential, which represents the voltage between the right arm and the left leg, providing valuable information about the timing and duration of each phase of the cardiac cycle.