A fist-sized pump still tops the global death tables
The heart is a muscular pump driving blood through vessels that together make the circulatory system. In humans four chambers—two atria, two ventricles—beat to a sinoatrial pacemaker. Cardiovascular diseases caused about 19.8 million deaths in 2022, roughly thirty-two percent of deaths worldwide.
The human heart sits in the mediastinum between the lungs, level with thoracic vertebrae T5 to T8, inside a double-layered, fluid-filled pericardial sac. It is cone-shaped, with its apex pointing down and left, 8 to 9 centimetres from the midline between the fourth and fifth ribs. An adult heart weighs 250 to 350 grams. The familiar comparison to a fist, about 12 by 8 by 6 centimetres, is disputed because the real organ is probably slightly bigger, and trained athletes can develop much larger hearts. Room for it comes at a cost: the left lung is smaller than the right and carries a cardiac notch.
A fibrous skeleton of collagen gives the heart its shape, forms rings for the four valves and, because collagen cannot carry current, electrically insulates the atria from the ventricles. The wall between the ventricles is far thicker than the one between the atria, since the lower chambers must build more pressure. The tricuspid valve, with three cusps, guards the right side and the two-cusped mitral valve the left, both tethered by chordae tendineae to papillary muscles.
Each beat starts in the sinoatrial node and spreads through the atrioventricular node and the conduction system, at a resting rate near 72 per minute in adults. Oxygen-poor blood arrives from the venae cavae into the right atrium, passes to the right ventricle and goes to the lungs; oxygenated blood returns to the left atrium and the left ventricle drives it out through the aorta to arteries, arterioles and capillaries. In the rare condition dextrocardia the heart lies to the right.
Cardiovascular disease is the world's leading killer, and heart attacks and strokes account for 85 percent of those deaths. Risk rises with smoking, excess weight, inactivity, high cholesterol, high blood pressure and poorly controlled diabetes. Symptoms are often absent, so doctors rely on history, the stethoscope, ECGs and ultrasound echocardiograms.
Source: Heart
