A fist-sized, cone-shaped muscular organ lying two-thirds to the left of the midline of the chest
Heart — sits in the middle mediastinum, inside its own sac.
Anatomy · Heart & blood vessels
Heart
Four chambers, about 100,000 beats a day
Thorax · middle mediastinum
A cone-shaped muscular pump about the size of a closed fist, lying in the middle mediastinum with roughly two-thirds of its bulk to the left of the midline. Its right side sends deoxygenated blood to the lungs and its left side sends oxygenated blood to the whole body, and four valves keep the flow one-way.
How to spot them
- ▸Cone shape with the blunt apex pointing down, forward and to the left
- ▸Two thin-walled auricles (ear-like flaps) sitting on top of the great vessels
- ▸Coronary arteries running in the grooves on its surface, with fat in the grooves
- ▸Most of the front face is right ventricle; the aorta and pulmonary trunk leave from the top
What to know
Its pointed tip can be felt beating against the chest wall in the fifth intercostal space, in line with the middle of the collarbone
Heart — the apex beat, formed by the left ventricle.
Four chambers arranged as two side-by-side pumps in series, one serving the lungs and one serving the rest of the body
Heart — right side pulmonary circuit, left side systemic circuit.
An organ whose wall has three layers: endocardium, myocardium and epicardium
Heart — the epicardium is also the visceral layer of the pericardium.
The 'lub-dub' heard through a stethoscope is the sound of its valves snapping shut
Heart — first sound from the atrioventricular valves, second from the aortic and pulmonary valves.
An organ that beats roughly 100,000 times a day and moves about five litres a minute at rest
Heart — around 2.5 to 3 billion beats in a lifetime.
Its own blood supply comes from two vessels arising just above the aortic valve and lying in grooves on its surface
Heart — the right and left coronary arteries.
Key ideas
- Two circuits in series: right side to the lungs (pulmonary), left side to the body (systemic). The left side generates far more pressure, hence its thicker wall.
- Valves open and close passively with pressure differences; no muscle opens them.
Quick-fire facts
- •Adult heart weighs roughly 250–350 g and is about the size of the owner's clenched fist.
- •Four chambers: right atrium, right ventricle, left atrium, left ventricle.
- •Four valves: tricuspid, pulmonary, mitral (bicuspid) and aortic.
- •The apex is formed by the left ventricle; the right border by the right atrium.
- •It is enclosed in the pericardium, a double-layered sac holding a thin film of lubricating fluid.
- •Resting cardiac output in a healthy adult is about 5 litres per minute.
- •The wall's layers, from inside out, are endocardium, myocardium and epicardium.
- •Cardiac muscle cells are joined end-to-end by intercalated discs, letting the wall contract as one.
- •The pacemaker is the sinoatrial node in the right atrium.
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Sources
- OpenStax — 19.1 Heart Anatomy — Anatomy and Physiology 2e
- TeachMeAnatomy — Heart Anatomy: Chambers, Valves, Conducting System and Coronary Supply