It is intended to provide novel polypeptides which specifically inhibit the activity of a mechano-sensitive channel; and mechano-sensitive channel inhibitors or remedies for atrial fibrillation containing these polypeptides or salts thereof. The above objects can be achieved by using polypeptides having amino acid sequences represented by SEQ ID NO:I (TVPOO3), SEQ ID NO:2 (TVPOO4) and SEQ ID NO:3 (TVPOO5), salts of these polypeptides, and mechano-sensitive channel inhibitors or remedies for atrial fibrillation containing the same.