AbstractIntroductionMyxomatous mitral valve degeneration (MMVD) is an acquired heart disease which sometimes result in pulmonary oedema and left atrial rupture. In previous reports, left atrial rupture has been non‐surgically controlled and its prognosis investigated. There is, however, no report concerning surgically treated left atrial rupture with mitral valvuloplasty and follow‐up results.ObjectivesThis report aimed to develop a surgical strategy for a case of left atrial rupture caused by MMVD.Materials and methodsThree dogs were presented at a private hospital for surgical treatment of MMVD. All three dogs had a previous history of left atrial rupture due to MMVD. The left atrium rapture was diagnosed from indicating that characteristics of the drained pericardial effusion consistent with blood. Mitral valvuloplasty was performed in all dogs using an extracorporeal circulation machine, and the surgical procedure was modified according to each case. In cases with severe adhesion between the pericardial and left atrial appendage, suturing of the left atrial appendage was performed strategically. Additionally, in cases with severe hypotension caused by left atrial rupture, cardiopulmonary bypass was started as soon as possible during the surgical procedure.Discussion and ConclusionSince the haemodynamics of all dogs had improved, and the owner reported no cardiac‐related clinical signs, all drugs were withdrawn 3 months after surgery. Since left atrial rupture due to MMVD can cause hypotension, cardiopulmonary bypass should be started as soon as possible during the surgical procedure to maintain the blood pressure and suturing of the left atrial appendage should be performed strategically.