Heart

The most important organ in the body and a complex pump that is responsible for blood, oxygen and nutrients circulation.

The heart is a vital muscular organ that is hollow and cone-shaped. It is about the size of an adult's fist and is typically located to the left of the breastbone. All vertebrates have a heart that is responsible for pumping blood through the "passage ways" or blood vessels. A vertebrate's heart is composed of an involuntary muscle tissue that is only found within this vital organ, known as the cardiac muscle. Cardiac is a related term that is derived from the Greek word kardia, which means heart. The average weight of a human heart is 300 grams to 350 grams in males, and 250 grams to 300 grams in females.

A human heart, on the average, beats 72 times per minute and approximately 2.5 billion times in a lifetime [at around 66 years]. An electrical pacemaker or the group of cells which are capable of generating electrical activity in the heart triggers every heartbeat. These cells create electrical impulses that are meant to spread over the heart and let it contract. The heart's largest natural pacemaker is called the SA or sinoatrial node. It is located in the right atrium and specialized cells from it carry the electrical charge which directs them to the rest of the heart.

Every heart has three layers namely: endocardium, myocardium and pericardium. It is divided into four chambers: right and left atrium on the upper chambers, and right and left ventricles on the lower chambers. The septum, which is a muscular wall, separates the left and right sides of the heart. Each chamber has a valve: tricuspid valve at the exit of the right atrium, mitral valve for the left atrium, pulmonary valve at the exit of the right ventricle, and the aortic valve at the exit of the left ventricle.

The heart works by contracting the muscles in two stages so that blood is squeezed out. This stage is known as systole. Once the heart relaxes, it is known as diastole. The heart is filled up with blood again and the entire process is repeated over and over at a fraction of a second.