Objective: Aim To investigate the role of the ligament of Marshall(LOM) in the development of atrial fibrillation(AF) in canines and to find an electrical isolation method.Methods:Intervention in LOM was carried out in 20 normal healthy canines.The animals were divided into 2 groups according to the method of intervention: Group A

7 dogs was intervened by cutting its proximal segment near coronary sinus;Group B

the dogs were ablated with ethanol.The inducing rate of AF was statistically analyzed in each group and between two groups pro and post isolation respectively.Results:In group A

before intervention the inducing rate of AF was 85.7%(6/7).After the procedures

the rate was 71.4%(5/7)

the inducing rate pro and post intervention presented no significant difference in this group at P>0.05.In Group B

the inducing rate was 81.8 %(9/11) before intervention

while post intervention the rate was 9.1 %(1/11)

the difference of inducing rate pro and post intervention was statistically significant at P<0.01.The inducing rate of AF from both groups was statistically analyzed pro and post intervention

and the difference presented no significant at P>0.05 before intervention

the difference was significant at P<0.05 after intervention.Conclusions:LOM plays an essential role in the development of atrial fibrillation in canines.The critical ablation site may be the entrance of the LOM to the coronary sinus and/or left atria;the end of the ablation is totally disappearing of LOM potentials.