Heart
The heart is a hollow organ located approximately in the center of your chest and is about the size of your fist. It is made of special muscle tissue called myocardium, and it constantly pumps blood throughout your body. The heart is divided into four chambers. The two upper chambers (the right and left atria) receive and collect blood coming into the heart from the body. The two lower chambers (the right and left ventricles) pump blood out to the body. The four chambers are separated by one-way valves that keep the blood from flowing backwards. The atria and ventricles work together to circulate blood, delivering oxygen and nutrients to the entire body. | 