Minimal access techniques with cardiopulmonary bypass use smaller cannula systems for management of cardiopulmonary bypass. To augment flow rates through the smaller cannula, the technique of vacuum-assisted venous drainage has been used. We describe a complication of vacuum-assisted venous drainage by inadvertent positive pressurization of the venous circuit resulting in a paradoxic air embolus across a patent atrial septal defect. Hazards of the current cardiopulmonary bypass systems and techniques for avoiding this potential complication are discussed.