A medical instrument used to assess cardiac function by measuring the electrical activity of the heart. With each heartbeat, an electrical signal spreads from the top of the heart to the bottom. As it travels, the signal causes the heart to contract and pump blood and sets the rhythm of the heartbeat. The process repeats with each new heartbeat. ECG detects these signals with electrodes that are placed on the body. It shows how fast the heart is beating, whether the rhythm of the heartbeat is steady or irregular, and the strength and timing of electrical signals as they pass through each part of the heart.