National Academy of Sports Medicine (NASM) Group Fitness Instructor Practice Exam

A primary function of a heart valve is to prevent backflow of blood. Heart valves are critical components of the cardiovascular system, designed to ensure that blood flows in the correct direction through the heart and into the vessels. Each valve opens to allow blood to flow from one chamber of the heart to another or into the arteries, and then closes to prevent any reverse flow. This one-way function is essential for maintaining efficient circulation and ensuring that oxygenated and deoxygenated blood do not mix.

Additionally, while promoting blood flow and increasing blood pressure are important aspects of circulatory function, these actions are primarily the result of heart contractions and the muscular activity of the heart, not the valves themselves. Filtering blood impurities is a function carried out by other organs like the kidneys and does not pertain to heart valves. Thus, the correct answer highlights the essential role of heart valves in maintaining proper blood flow and pressure in the circulatory system by preventing backflow.