The heart is a muscular organ in humans and other animals, which pumps blood through the blood vessels of the circulatory system.

The circulatory system, also called the cardiovascular system or the vascular system, is an organ system that permits blood to circulate and transport nutrients, oxygen, carbon dioxide, hormones, and blood cells to and from the cells in the body to provide nourishment and help in fighting diseases, stabilize temperature and pH, and maintain homeostasis.

Blood is a body fluid in humans and other animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells.

Animals are multicellular, eukaryotic organisms of the kingdom Animalia.

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Blood provides the body with oxygen and nutrients, as well as assists in the removal of metabolic wastes.

Metabolic wastes or excretes are substances left over from metabolic processes, which cannot be used by the organism, and must therefore be excreted.

A nutrient is a component in foods that an organism uses to survive and grow.

Oxygen is a chemical element with symbol O and atomic number 8.

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The heart is located in the middle compartment of the chest.

The thorax or chest is a part of the anatomy of humans and various other animals located between the neck and the abdomen.


In humans, other mammals, and birds, the heart is divided into four chambers: upper left and right atria; and lower left and right ventricles.

Birds are a group of endothermic vertebrates, characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweight skeleton.

Mammals are any vertebrates within the class Mammalia, a clade of endothermic amniotes distinguished from reptiles and birds by the possession of a neocortex, hair, three middle ear bones and mammary glands.


Commonly the right atrium and ventricle are referred together as the right heart and their left counterparts as the left heart.


Fish in contrast have two chambers, an atrium and a ventricle, while reptiles have three chambers.

Reptiles are tetrapod animals in the class Reptilia, comprising today's turtles, crocodilians, snakes, amphisbaenians, lizards, tuatara, and their extinct relatives.


In a healthy heart blood flows one way through the heart due to heart valves, which prevent backflow.

A heart valve normally allows blood to flow in only one direction through the heart.


The heart is enclosed in a protective sac, the pericardium, which also contains a small amount of fluid.

The pericardium is a double-walled sac containing the heart and the roots of the great vessels.


The wall of the heart is made up of three layers: epicardium, myocardium, and endocardium.

Cardiac muscle is an involuntary, striated muscle that is found in the walls and histological foundation of the heart, specifically the myocardium.

The endocardium is the innermost layer of tissue that lines the chambers of the heart.


The heart pumps blood with a rhythm determined by a group of pacemaking cells in the sinoatrial node.


These generate a current that causes contraction of the heart, traveling through the atrioventricular node and along the conduction system of the heart.

The electrical conduction system of the heart transmits signals generated usually by the sinoatrial node to cause contraction of the heart muscle.

The atrioventricular node, or AV node is a part of the electrical conduction system of the heart that coordinates the top of the heart.


The heart receives blood low in oxygen from the systemic circulation, which enters the right atrium from the superior and inferior venae cavae and passes to the right ventricle.


From here it is pumped into the pulmonary circulation, through the lungs where it receives oxygen and gives off carbon dioxide.

The pulmonary circulation is the portion of the circulatory system which carries deoxygenated blood away from the right ventricle of the heart, to the lungs, and returns oxygenated blood to the left atrium and ventricle of the heart.

The lungs are the primary organs of respiration in humans and many other animals including a few fish and some snails.

Carbon dioxide is a colorless and odorless gas vital to life on Earth.


Oxygenated blood then returns to the left atrium, passes through the left ventricle and is pumped out through the aorta to the systemic circulation−where the oxygen is used and metabolized to carbon dioxide.

The aorta is the main artery in the human body, originating from the left ventricle of the heart and extending down to the abdomen, where it splits into two smaller arteries.

Metabolism is the set of life-sustaining chemical transformations within the cells of organisms.


The heart beats at a resting rate close to 72 beats per minute.

In musical terminology, tempo [ˈtɛmpo] is the speed or pace of a given piece.


Exercise temporarily increases the rate, but lowers resting heart rate in the long term, and is good for heart health.


Cardiovascular diseases are the most common cause of death globally as of 2008, accounting for 30% of deaths.


Of these more than three quarters are a result of coronary artery disease and stroke.

Coronary artery disease, also known as ischemic heart disease, is a group of diseases that includes: stable angina, unstable angina, myocardial infarction, and sudden cardiac death.

Stroke is when poor blood flow to the brain results in cell death.


Risk factors include: smoking, being overweight, little exercise, high cholesterol, high blood pressure, and poorly controlled diabetes, among others.

Diabetes mellitus, commonly referred to as diabetes, is a group of metabolic diseases in which there are high blood sugar levels over a prolonged period.

Hypertension, also known as high blood pressure, is a long-term medical condition in which the blood pressure in the arteries is persistently elevated.

Smoking is a practice in which a substance is burned and the resulting smoke breathed in to be tasted and absorbed into the bloodstream.


Cardiovascular diseases frequently have no symptoms or may cause chest pain or shortness of breath.

Chest pain may be a symptom of a number of serious disorders and is, in general, considered a medical emergency.

Shortness of breath, also known as dyspnea, is a feeling like one cannot breathe well enough.

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