Mechanism of external chest compression Chest pump sequential increased and decreased pressure in the thoracic cavity valves maintaining forward direction of flow Cardiac pump -sequential filling and emptying of cardiac chambers -valves maintaining forward direction of flowMechanism of external chest compression • Chest pump - sequential increased and decreased pressure in the thoracic cavity - valves maintaining forward direction of flow • Cardiac pump -sequential filling and emptying of cardiac chambers -valves maintaining forward direction of flow