What does an EKG record regarding heart function?

An EKG, or electrocardiogram, specifically records the electrical impulses generated by the heart as it beats. This electrical activity reflects the cardiac cycle, showing how the heart's electrical signals initiate muscle contractions, thereby enabling the heart to pump blood effectively. The EKG provides insights into the rhythm, rate, and overall electrical activity of the heart, which is essential for diagnosing various cardiac conditions.

The other options do not accurately describe what an EKG measures. While the heart's muscle contractions are influenced by the electrical impulses, the EKG itself does not capture the contractions directly but rather the signals that lead to them. Similarly, the EKG does not measure electrical currents in the body outside of the heart or assess oxygen levels in the bloodstream; these are different assessments performed through other diagnostic tests.