Which of the following best defines fibrillation?

Fibrillation refers to the condition where the heart experiences unorganized, random contractions. In this state, the electrical signals that trigger heartbeats become erratic, preventing the heart chambers from contracting effectively. This can lead to insufficient blood flow and, in severe cases, may result in cardiac arrest if not addressed promptly.

The other choices emphasize organized and coordinated heart activity, which is the opposite of what fibrillation entails. While calm or controlled heartbeats signify a properly functioning heart rhythm, fibrillation disrupts this harmony, leading to a chaotic arrangement of heart contractions. An accelerated heartbeat, while it may sometimes occur in other contexts related to heart activity, does not accurately capture the essence of fibrillation, which is primarily characterized by disorganization rather than mere speed or rapidity. Therefore, the definition that aligns with the characteristics of fibrillation is the description of unorganized, random heart contractions.