Final answer:
CPR should be started immediately when a patient is in cardiac arrest.
Step-by-step explanation:
When a patient is in cardiac arrest, it is crucial to begin CPR immediately. Cardiopulmonary resuscitation (CPR) involves manually compressing the heart to push blood into the pulmonary and systemic circuits. High-quality chest compressions should be performed until the patient regains spontaneous contraction or is declared dead by a healthcare professional.