Normal resting heart rates range from 60â100 bpm. Bradycardia is defined as a resting heart rate below 60 bpm. However, heart rates from 50 to 60 bpm are common among healthy people and do not necessarily require special attention.achycardia is a fast heart rate, defined as above 100 bpm at rest. Bradycardia is a slow heart rate, defined as below 60 bpm at rest. During sleep a slow heartbeat with rates around 40â50 BPM is common and is considered normal.
The adrenergic receptors (or adrenoceptors) are a class of G protein-coupled receptors that are targets of the catecholamines, especially norepinephrine (noradrenaline) and epinephrine (adrenaline).
Beta blockers block the action of endogenous catecholamines epinephrine (adrenaline) and norepinephrine (noradrenaline) -in particular on adrenergic beta receptors, of the sympathetic nervous system, which mediates the fight-or-flight response.hree types of beta receptors are known, designated Î² 1, Î² 2 and Î² 3 receptors. Î²1-adrenergic receptors are located mainly in the heart and in the kidneys. Î²2-adrenergic receptors are located mainly in the lungs, gastrointestinal tract, liver, uterus, vascular smooth muscle, and skeletal muscle.