What is heart rate a measure of?

Heart rate specifically refers to the number of times the heart beats within a minute, which is expressed in beats per minute (BPM). This measurement reflects the frequency of the heart's contractions, which is vital for determining cardiac function and overall cardiovascular health.

Monitoring heart rate can provide insights into how well the heart is performing in relation to physical activity, stress, and overall fitness levels. It indicates how effectively the heart is able to pump blood throughout the body, which is essential for delivering oxygen and nutrients to tissues.

In contrast to this, other choices refer to different physiological concepts. For example, the force of blood against the heart valves relates more to the mechanics of heart operation than to heart rate itself, while the volume of blood pumped by the heart refers to stroke volume or cardiac output, which is a different measure than heart rate. The pressure within the arteries relates to blood pressure measurements, an entirely separate metric that indicates how forcefully the blood is exerting pressure against arterial walls. Thus, option B is the most accurate and relevant definition for heart rate.