PITX2 and atrial fibrillation: The ionic mechanisms of Pitx2 deficiency-induced AF were investigated by examining calcium transient (Cai) and action potentials (APs) using the computer models of control and four different scenarios of Pitx2-deficiency (Pitx2-1, Pitx2-2, Pitx2-3 and Pitx2-4) (Fig 2).