1. The skeletal muscle pump
Veins are surrounded by large skeletal muscles which compress the veins when they contract, increasing venous pressure and forcing blood to flow towards the heart. When the skeletal muscles relax the valves prevent backflow.

2. The thoracic pump
Pressure changes in the thorax during respiration also assist venous return. During inspiration the negative intrathoracic pressure draws blood into the thoracic veins.