The primary organ in the circulatory system responsible for pumping blood is the heart. This muscular organ contracts rhythmically to circulate blood throughout the body, delivering oxygen and nutrients while removing waste products. The heart is divided into four chambers: two atria and two ventricles, each playing a vital role in maintaining efficient blood flow. Proper functioning of the heart is crucial for sustaining life, as it supports the overall circulation necessary for the body’s metabolic activities.