Heart

At one time, people thought that the heart was the seat of love, desire, courage, and bravery. Today it is known that these feelings are based in the brain. The fist sized, cone shaped heart is a muscular pump that contracts every second to send the blood flowing through the body's network of blood vessels. Slightly to the left, the heart lies anterior to the backbone and posterior to the sternum, and is surrounded and partially overlapped by the two lungs. The heart tissue is unique in that it can contract tirelessly without ceasing and has the ability to change its pumping speed and force to match the body's needs. Daily it beats about 10,000 times.

Did you know?-----
The heart beats about 10,000 times daily and in the life of about 70 years for about 2.5 billion times without stopping.

     The heart is surrounded externally by a tough double membrane, the pericardium. Internally the heart is divided by a thick muscular septum into the right and left sides. Each half has a smaller chamber called an atrium that receives blood and pumps it into the bigger, thicker walled ventricle below. The right atrium receives oxygen-poor blood from the body through the inferior and superior vena cava. The left atrium receives oxygen-rich blood from the lungs through the pulmonary veins. The ventricles pump blood out of the heart. The right ventricle pumps, oxygen-poor blood through the pulmonary trunk and arteries to the lungs, the left pumps oxygen-rich blood to the body through the aorta. The heart valves see to it that the blood flows in the right direction, when the muscles contract.

Cardiac Cycle: The beat though feels like a single contraction, is actually made of three phases that occur in a timed sequence called cardiac cycle taking about 0.8 seconds at rest.