Final answer:
CPR should be initiated when the heart of a person stops pumping blood or pumps blood so poorly that vital organs can no longer function. It involves applying pressure to the sternum to manually compress the blood within the heart.
Step-by-step explanation:
CPR should be initiated when the heart of a person stops pumping blood or pumps blood so poorly that vital organs can no longer function. It is a medical emergency that requires immediate intervention. CPR involves applying pressure to the sternum in the area between the lines at T4 and T9 to manually compress the blood within the heart and push some of the blood into the pulmonary and systemic circuits. The goal is to maintain blood flow until the heart resumes beating or until the patient is declared dead by a healthcare professional.