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Atrial fibrillation (abnormal heart rhythm) is associated with shorter action potential duration and believed to be affected by the G protein-gated K+ channel, IK,ACh. The IK,ACh channel, when activated by G proteins, allows for the flow of K+ across the plasma membrane and out of the cell. This current hyperpolarizes the cell, thus terminating the action potential. It has been shown that in chronic atrial fibrillation there an increase in this inwardly rectifying current because of constantly activated IK,ACh channels. Increase in the current results in shorter action potential duration experienced in chronic atrial fibrillation and leads to the subsequent fibrillating of the cardiac muscle. Blocking IK,ACh channel activity could be a therapeutic target in atrial fibrillation and is an area under study.