What does an EKG primarily measure?

An EKG, or electrocardiogram, primarily measures the electrical activity of the heart. It records the electrical impulses that trigger each heartbeat, providing important information about the heart's rhythm, rate, and the size and position of the heart chambers. This electrical activity is crucial for diagnosing a variety of cardiac conditions, including arrhythmias, heart attacks, and other heart diseases.

The other options refer to different physiological measurements. Blood pressure (the first option) relates to the force of blood against the walls of arteries, while body temperature (the third option) indicates the body's thermal state. The level of oxygen in the blood (the fourth option) is typically assessed using a pulse oximeter rather than an EKG. Each of these measurements serves a different purpose in patient assessment, but it is the electrical activity that is directly captured by an EKG.