What risks are attributed to untreated bradycardia or tachycardia?

Tachy or Brady: Aside from not feeling well with either of these, there is a likelihood that either can cause a cardiomyopathy or a weakness in the muscle. These rhythms can also cause a loss of consciousness or syncope. So, these arrhythmias should be treated and followed regularly.

Pump Failure: Heart rate & rhythm combine to determine cardiac output, or, in common terms, the pumping ability of the heart. Good cardiac function & pumping ability in a normal heart can decrease with slow or fast heart rates. Usually, low rates protect the heart, but limit cardiac output = exercise tolerance is decreased. Sustained high rates = heart damage & heart failure. Sick heart? All bets are off. Dr. M.

It depends: In some cases, these can be normal states (an athletic person with bradycardia) or due to another condition (tachycardia with overactive thyroid, too much alcohol, or anemia) that needs to be treated. Otherwise, either can cause dizziness or fainting, fatigue, and inadequate blood flow (which can cause heart damage or even a stroke). The safest approach is treatment.