Our institution experienced two bypass cases from January through December 2011 in which venous return was significantly variable and at times poor. Luminal clot formation in the venous cannulae was found in each case postbypass. These events were captured and monitored through our institution's Non-Routine Event Reporting Program and eventually reported to the Food and Drug Administration (FDA). We began inspecting all venous cannulae postbypass in December 2011. During a subsequent 9-month surveillance period, we documented 33 venous cannulae in 21 patients with luminal clot formation. Only one cannula during this surveillance period required change-out on bypass. The manufacturer eventually identified changes in production that likely caused the clotting events. The manufacturer modified their production methods and began supplying cannulae produced under the new method in September 2012. We have experienced only one clotting event with the new cannulae and in that instance, the metal tip was found to be defective. We recommend inspection of all venous cannulae postbypass with internal, manufacturer, and FDA reporting for those noted to have luminal clot formation.