Iatrogenic aortic dissection is a rare and serious complication of cardiac surgery with an incidence between 0.12' and 0.16'. Dissections involving an intimal flap can be detected using trans-esophageal echocardiography (TEE) with a sensitivity of 94'-100' and specificity of 77'-100'. Rarely, dissections can occur that are not detectable by TEE. There have been reports of iatrogenic dissection in the ascending aortic cannulation site; however, a dissection at the antegrade cardioplegia cannulation site is very rare. It also presents challenges associated with early diagnosis and appropriate intervention. We are describing a rare case of aortic dissection at the antegrade cardioplegia cannulation site in the proximal ascending aorta. The dissection was unable to be visualized with TEE initially, and required epi-aortic ultrasound to diagnose dissection in timely manner.