Other electrical effects include an initial brief increase in action potential, followed by a decrease as the K+ conductance increases due to an increased intracellular amounts of Ca2+ ions. The refractory period of the atria and ventricles is decreased, while it increases in the sinoatrial and AV nodes. A less negative resting membrane potential is made, leading to increased irritability. Other, more indirect effects are cholinomimetic because of vagal stimulation, giving rise to AV nodal delay.