A 2-month-old male suddenly developed mitral regurgitation aggravation while waiting for surgical repair of aortic coarctation. There were no signs of infection or history of trauma. Emergency surgery was performed, during which rupture of chordae tendineae of the A2 portion of the anterior mitral leaflet was confirmed. At last follow-up, 11 months postsurgery, the patient was in an acceptable state, with continuing moderate mitral valve regurgitation. This case demonstrates an unusual but dangerous natural course of aortic coarctation and suggests an additional basis of urgent repair of aortic coarctation.