venous reservoirs are interposed between the patient and the arterial pump and serve to remove air bubbles and provide compliance that accommodates variations in the volume of blood circulating in the extracorporeal circuit during cardiopulmonary bypass . venous drainage by gravity alone provides an inadequate rate of blood return during procedures such as minimally invasive cardiac surgery and bypass via femoral cannulation . in these cases the resistance of the venous cannula limits the maximum achievable flow . vacuum assisted venous drainage is a technique that overcomes flow limitations by applying suction to venous blood thereby increasing the pressure difference between the venous site and venous reservoir . prior art venous bags cannot be used with vavd unless a more expensive and complicated two - pump system is used . the present invention describes a soft - shell venous reservoir that allows vavd using a single pump . the invention describes a soft shell reservoir that is sealed within a , preferably , clear rigid housing . a gas port connected to the space between the bag and rigid housing is used to adjust the pressure within that space : it allows the user to adjust the “ atmospheric ” pressure about the external walls of the soft - shell reservoir . another aspect of the invention improves gas bubble removal . one form of the invention also incorporates means that improve gas bubble removal from blood transiting the collapsible reservoir . in another form of the invention the venous bag has all its ports extending from its top , an innovation that provides easy loading / unloading of the reservoir in / out of its holder and simplifies sealing the reservoir in a chamber thereby allowing the aforementioned vavd .