Define cardiac arrest.

Cardiac arrest specifically refers to a condition in which the heart has stopped beating effectively, resulting in the absence of a pulse and the cessation of breathing. This critical situation is characterized by the failure of the heart to pump blood, which can lead to death if not treated promptly.

When a person is in cardiac arrest, they will not exhibit signs of circulation, meaning there will be no pulse detectable at major arteries. Additionally, without effective heart function, oxygenated blood is not delivered to the brain and other vital organs, leading to loss of consciousness and respiratory failure. The urgency of recognizing cardiac arrest lies in the necessity of immediate intervention, such as CPR and defibrillation, to restore normal heart function and increase the chances of survival.

The other options describe different medical conditions or symptoms but do not accurately define cardiac arrest. For instance, unconsciousness with a weak pulse or irregular heartbeat indicates other cardiac issues, while difficulty breathing and fainting can result from various causes not limited to cardiac arrest.