when ach binds to muscarinic receptors in cardiac muscles the
Muscarinic acetylcholine receptor The M2 muscarinic receptors are located in the heart, where they act to slow the heart rate down to normal sinus rhythm, by slowing the speed of depolarization. In humans under resting conditions vagal activity dominates over sympathetic activity. Hence inhibition of m2 receptors (e.g. by atropine) will cause a raise in heart rate. They also moderately reduce contractile forces of the atrial cardiac muscle, and reduce conduction velocity of the atrioventricular node (AV node). It also serves to slightly decrease the contractile forces of the ventricular muscle.