As the exercise progresses, muscular activity increases venous return. This increases the pre-load on the right ventricle. During venous exercise, the rhythmic pump of the muscles facilitates venous return by forcing the blood through one way valves that lead to the heart. Additionally, increased lung activity which creates a change in thoracic pressure that draws blood towards the heart. Regular exercises improves the venous return by increasing total blood volume, increasing end diastolic volume and increasing the size and contractile strength of the heart muscle.