What does an electrocardiogram record?

An electrocardiogram (ECG or EKG) specifically records the electrical activity of the myocardium, which is the muscular tissue of the heart. This activity is produced by the conduction system of the heart, where electrical impulses initiate each heartbeat and control the heart’s rhythm. By capturing this electrical activity, healthcare professionals can assess heart function, diagnose various cardiac conditions, and monitor the heart's health over time. An ECG provides critical insights into how well the heart is functioning, including the heart rate, rhythm, and the presence of any abnormalities.

The other options are not relevant to what an electrocardiogram measures. For example, while blood flow and circulation are important in cardiology, they are not directly captured by an ECG. Similarly, the physical structure of the heart may be assessed through imaging techniques but is not the purpose of an electrocardiogram. The focus of the ECG is purely on the electrical signals that indicate the performance of the heart muscle.