HSPB1 and atrial fibrillation: Remarkably, HSPB1 levels were found to be increased in atrial tissue samples (from the right atrial appendage [RAA] and left atrial appendage [LAA]) of patients with PAF; however, these levels are exhausted in patients with longstanding persistent AF,71 indicating that low RAA and LAA HSPB1 levels are associated with AF progression.