What procedure is used to trace the electrical activity of the heart?

The procedure used to trace the electrical activity of the heart is an electrocardiogram (EKG or ECG). This test records the electrical signals that trigger each heartbeat, allowing for the assessment of heart rhythm, heart rate, and the size and position of the heart chambers. By placing electrodes on the skin, the EKG measures the electrical impulses in the heart over a specific duration, producing a graphical representation of the heart's activity.

The other options, while important in their own right, do not measure electrical activity. X-rays provide images of the heart's structure and can identify problems with the heart's physical condition but do not provide information about the heart’s electrical functioning. Ultrasound, or echocardiography, uses sound waves to create images of the heart and assess its movement and structure, but again, it does not trace electrical activity. CT scans offer detailed images of the heart and surrounding structures, useful for diagnosing certain conditions, but they do not measure electrical impulses. Hence, the EKG is the specific procedure designed for tracing the electrical activity of the heart.