Most people are familiar with the artificial heart pacemakers that we use to keep the heart beating, but many don’t realize that the body has built-in heart pacemakers of its own. Every cardiac cell is capable of automaticity (to fire on its own) and conductivity, but there is a specialized network in charge.
The heart’s conduction system includes areas of bundled electrical fibers we call "nodes," as well as specialized fibers that line the two lower chambers (ventricles) and have enough "electrical potential" to initiate contractions or heart beats. In case your doctor or health-care provider has used any of these terms with you, here some a basic explanation.
Your Natural Heart Pacemaker
We look first to the "sinus node," which is up atop the inside of the right atrium in the coronary "sinus," not unlike a nasal sinus. This sino-atrial node is also called the "SA node," and has the huge responsibility to stimulate each and every heart beat for a lifetime. Not even a lunch break for the SA node!
The SA node normally "fires" an impulse between 60 and 100 beats per minute (bpm). Heart rates over the "intrinsic" or "built in" rate of each heart pacemaker are generally referred to as tachycardias—"tachy" being Latin for "speed," like a tachometer measures speed.
SA node-generated heart rates below normal range (<60bpm), are referred to as bradycardias, with "brady" meaning slow (although my 2-year-old grandson Brady is anything but!).
Some people experience symptoms with tachycardia and bradycardias, such as nausea, lightheadness, dizziness—and even loss of consciousness if the heart pumps exceedingly slow or so fast that it’s less effective.
Symptoms of tachycardias and bradycardias are usually related to age, physical condition, the actual heart rate and personal tolerance. A very fit athlete, for example, may be quite healthy with heart rates less than 60, whereas someone else—especially an elderly person—may be quite symptomatic.