occurs in regular atrial cardiac myocyte membrane repolarization cardiac muscle cell membrane repolarization atrial cardiac muscle cell membrane repolarization GO:0099624 biological_process The process in which ions are transported across the plasma membrane of an atrial cardiac muscle cell such that the membrane potential changes in the repolarizing direction, toward the steady state potential. For example, the repolarization during an action potential is from a positive membrane potential towards a negative resting potential.