Ion channels and pathways of greatest importance for the generation of the action potential and thus for the heart rate: f-channel (sodium channels If), cholinergic calcium channel (IK,ACh), non-transmitter dependent potassium channel (IK), L-type (long lasting) calcium channel (ICa,L) T-type (transient) calcium channel (ICa,T), calcium-sodium exchange channel (INCX), inhibitory G-protein (Gi), stimulating G-protein (Gs), muscarinic receptor (M2), β1-receptor, cyclic AMP (cAMP), phosphorkinase A (PKA), and phosphordiesterase (PDE).