Final answer:
The skeletal muscle pump and the respiratory pump are two key factors that aid in the return of venous blood to the heart by maintaining a pressure gradient that encourages blood flow.
Step-by-step explanation:
The two factors that promote the return of venous blood to the heart are the skeletal muscle pump and the respiratory pump. The skeletal muscle pump enhances venous return by using the contraction of muscles surrounding the veins to 'milk' the blood towards the heart. Equally, the respiratory pump aids in venous return through the pressure changes in the thoracic cavity during respiration, which encourages blood flow towards the heart. Both of these mechanisms overcome the low pressure in the venous system and use physiological pumps to help maintain a pressure gradient that favors the movement of blood back to the heart.