Abstract: An autotransfusion device for use with a chest drainage unit is disclosed which includes a collapsible blood collection bag assembly having slotted stiffener members and a holder for holding the stiffener members bowed outwardly and the bag expanded for collecting blood. The bag assembly is removable from the holder for infusing the collected blood into the patient. An inlet and a gas outlet are at the top of the bag, and a filter is arranged to filter blood from the inlet to a blood collection portion of the bag, but air from the inlet can flow to the gas outlet without flowing through the filter.