Abstract Introduction: Left atrial dissection is a rare complication of cardiac surgery, most commonly associated with mitral valve surgery. Herein, we report on successful conservative treatment of left atrial dissection by avoiding anticoagulation. Case Report: A 64-year-old man developed left atrial dissection due to retrograde cardioplegia cannulation during operation for acute type A aortic dissection. As there was no connection between the left atrial dissection cavity and the left atrium on enhanced computed tomography, we did not administer anticoagulants to prevent expansion of the left atrial dissection cavity. However, the patient developed atrial fibrillation, which was successfully managed by beta-blocker and amiodarone administration. Follow-up imaging showed gradual left atrial dissection reduction, and the patient was started on anticoagulation therapy. Conclusion: We were able to resolve left atrial dissection by preventing the use of anticoagulation therapy in the acute stage by managing the atrial fibrillation with antiarrhythmic drugs.