Increased expression of Rho kinase (ROCK) and myosin-phosphatase-target subunit-1 (MYPT-1), ROCK activity’s marker, were shown in AF patients, which correlated with connexin 40 (Cx40) expression, membrane protein of heart gap junctions, key for rapid action potential’s cell–cell transfer. The gene discussed is PPP1R12A; the disease is atrial fibrillation.