Which of the following helps return blood to the heart?Multiple ChoiceEnd systolic volumeContracting skeletal musclesPositive pressure in thoracic cavityValves in the arteries

The correct answer is "Contracting skeletal muscles". Here's why:

1. End systolic volume: This is the volume of blood in a ventricle at the end of contraction, or systole, and the beginning of filling, or diastole. It doesn't directly help return blood to the heart.

2. Contracting skeletal muscles: When skeletal muscles contract during physical activity, they squeeze the blood vessels, pushing blood back towards the heart. This is known as the skeletal muscle pump and it's a crucial mechanism that assists in venous return to the heart.

3. Positive pressure in thoracic cavity: Positive pressure in the thoracic cavity actually hinders the return of blood to the heart. During inspiration, negative pressure is created which aids in the return of blood to the heart.

4. Valves in the arteries: Arteries carry blood away from the heart, not towards it. The valves in veins prevent backflow and assist in returning blood to the heart, not the valves in arteries.