What does heart rate measure?

Heart rate specifically measures the number of times the heart beats in one minute, which is often expressed in beats per minute (bpm). This metric provides a direct indication of how hard the heart is working and is a crucial parameter in assessing cardiovascular fitness and overall health. During exercise, for example, the heart rate typically increases to supply more oxygenated blood to the muscles, showing the body's response to physical demands.

The other options pertain to different cardiovascular functions. The amount of blood pumped by the heart in one minute is known as cardiac output, which is the product of heart rate and stroke volume. The total volume of blood in the circulatory system pertains to blood volume, an important aspect of overall body fluid management but not heart rate itself. Blood pressure measures the force of blood against arterial walls, which, while related to heart function, is distinct from the concept of heart rate. Each of these metrics provides valuable information, but heart rate alone is specifically focused on the frequency of heartbeats.