SMAD2 and atrial fibrillation: In vivo: AF inducibility↓, AF burden↓, atrial dominant frequency↓, Rotations↓, singularity points↓, P3NP↓, α‐SMA↓, fibrosis tissue area↓, Smad2/3↓, LA area↓, APD↑. In vitro: migration↓, proliferation↓