The heart is a muscular organ in most animals, which pumps blood through the blood vessels of the circulatory system. The blood supplies the body with oxygen and nutrients while helping to eliminate metabolic waste. In humans, the heart is located between the lungs, in the middle compartment of the chest.
In humans, other mammals and birds, the heart is divided into four cavities: upper left and right atria and lower left and right ventricles. Commonly the right atrium and the ventricle are called together the right heart and their left counterparts as the left heart. The fish, on the other hand, have two chambers, an atrium, and a ventricle, while the reptiles have three chambers. In a healthy heart, blood flows in one direction through the heart because of the heart valves, which prevent reflux. The heart is enclosed in a protective sac, the pericardium, which also contains a small amount of fluid. The heart wall is composed of three layers: epicardium, myocardium, and endocardium.
The heart pumps the blood with a rhythm determined by a group of pacing cells in the sinoatrial node. These generate a current that causes the heart to contract, moving through the atrioventricular node and along the conduction system of the heart. The heart receives oxygen-poor blood from the systemic circulation, which enters the right atrium through the superior and inferior vena cava and passes into the right ventricle. From there, it is pumped into the pulmonary circulation, through the lungs where it receives oxygen and releases carbon dioxide. The oxygenated blood then returns to the left atrium, passes through the left ventricle and is pumped through the aorta to the systemic circulation – where oxygen is used and metabolized to carbon dioxide. The heart beats at a speed of rest close to 72 beats per minute. Exercise temporarily increases heart rate, but lowers resting heart rate in the long term and is good for heart health. [ten]
Cardiovascular disease (CVD) is the most common cause of death in the world in 2008, accounting for 30% of deaths. Of these more than three quarters are a result of coronary heart disease and stroke. Risk factors include, but are not limited to, smoking, overweight, low exercise, high cholesterol, high blood pressure, and poorly controlled diabetes. Cardiovascular disease often has no symptoms or can cause chest pain or shortness of breath. The diagnosis of heart disease is often made by taking a medical history, listening to heart sounds with a stethoscope, an ECG and an ultrasound. Specialists who focus on heart disease are called cardiologists,