LAD is a rare complication of cardiac surgery, associated with mitral valve surgery in 0.16–0.84% of cases [1, 2]. Tsukui et al.  reported a case of LAD related to retrograde cardioplegia cannulation, but they performed surgical treatment for the LAD. Other causes of LAD include insertion of left ventricular vent tube, aortic dissection, among others. In our case, the most likely cause was the retrograde cardioplegia cannulation. The patient was diagnosed with ATAAD, but enhanced CT before operation did not show LAD. Furthermore, there was no resistance or any problems at insertion of the left ventricular vent tube. The hemodynamic effects of LAD vary widely, from asymptomatic to hemodynamic collapse [2, 3]. TEE, CT, magnetic resonance imaging, and catheter study are helpful for LAD detection and diagnosis. In our case, enhanced CT was useful for LAD diagnosis. This was our first experience of LAD, and we could not diagnose it during the operation. However, intraoperative diagnosis of LAD is desirable. Regarding LAD treatment, according to the literature, reversal of anticoagulation could prevent LAD expansion . In our case, follow-up CT demonstrated LAD resolution. However, in severe cases, surgical intervention should be considered. Currently, there are two types of surgical treatment: entry close and internal drainage . In the available reviews [2,3,4], the postoperative mortality rate was 9.8–12.7%; also the mortality rate of medical treatment was 11.2–13.8%. In our case, conservative therapy was fortunately successful, but if worsening developed, we would have considered an internal drainage procedure. Furthermore, there was fortunately no occurrence of stroke. However, if the AF persisted, we intended to use unfractionated heparin. The use of heparin is debatable as it might contribute to LAD expansion. If we had to use unfractionated heparin, we would have adjusted the activated partial thromboplastin time at 30–45 s. Enhanced CT enabled us to diagnose LAD, which we considered to be related to the retrograde cardioplegia cannulation. The coronary sinus is a low-pressure system; it might prevent inflow to the LAD cavity and LAD expansion. In addition, the LAD cavity had no connection with the left atrium, which indicated the possibility of preventing LAD expansion. In a recent review by Cereda et al. , the authors recommended conservative care in cases of stable LAD. In our case, we avoided anticoagulation drug administration by managing the AF with antiarrhythmic drugs. Thus, we selected conservative treatment.