Final answer:
The very rapid, irregular twitching of heart muscle fibers, known as fibrillation, can occur in the atria as atrial fibrillation or in the ventricles as ventricular fibrillation, which is a medical emergency. Defibrillation is the common treatment, and this condition may lead to arrhythmias.
Step-by-step explanation:
Very rapid, irregular contraction or twitching of the individual muscular fibers of the atria or ventricles is known as fibrillation. When this occurs in the atria, it is termed atrial fibrillation, and it is a serious condition. However, if this occurs in the ventricles, known as ventricular fibrillation, it constitutes a medical emergency as the ventricles are not effectively pumping blood, which can lead to brain death within minutes. Defibrillation is the most common treatment, involving the use of special paddles to apply a charge to the heart in an attempt to reestablish a normal rhythm. An untreated fibrillation condition may lead to an arrhythmia, a deviation from the normal heartbeat pattern, which is often diagnosed with the help of an electrocardiogram (ECG) or Holter monitor.