Background Same-day cancellations of cardiac surgery are unfortunate and costly occurrences that potentially place patients at risk of adverse events. Methods We retrospectively reviewed all same-day cancellations of cardiac operations requiring cardiopulmonary bypass from 2010 to 2012 at a large academic tertiary referral center. Results Of 7081 cardiac operations, 134 patients experienced 142 same-day cancellations of cardiac surgery. The foreseeable cancellation causes comprised 17% of cancellations, nonforeseeable 59%, and indeterminate 24%. The reasons for cancellation were medical (51%), administrative or scheduling (17%), unknown (12%), procedure no longer required (11%), patient cancellation (6%), and preincisional complication (3%). The mean interval from the patient seeing a nonsurgeon provider to cancellation was 8.6 ± 16.2 days. No statistically significant differences existed between the foreseeable and nonforeseeable cancellations and the timing of the visit to a nonsurgeon provider (15, 30, 45, and 60 days) before cancellation. Seven patients (5%) had died within 30 days of cancellation. Of those subsequently operated on, the mean interval from cancellation to performance of the operation was 12.2 ± 22.7 days. Of the 142 cancelled surgical procedures, 28 (20%) were never subsequently performed. Conclusions Same-day cancellation of cardiac surgery occurred infrequently (2% of cardiac operations performed) at our institution. The cancellations were for foreseeable causes in a few cases. Seeing a nonsurgeon provider more recently before cancellation was not significantly associated with nonforeseeable versus foreseeable cancellations. Although uncommon at our institution, same-day cancellations should be viewed as an opportunity for practice improvement, given the foreseeable nature of some cancelations, associated 30-day mortality, and portion of patients not subsequently undergoing cardiac surgery.