The heart
The heart is an organ that pumps blood around the body in a
double circulatory system : blood passes through the heart twice
on each circuit
The right ventricle pumps blood to the lungs , where gas
exchange takes place
The left ventricle pumps blood around the rest of the
body , so its wall is thicker, giving a higher pressure
Blood enters the atria, which contract to push it into the ventricles;
the ventricles contract to push it out through the arteries. Valves
stop blood flowing backwards
Vessel
Carries
From
To
Vena cava deoxygenated blood
body
right atrium
Pulmonary artery deoxygenated blood
right ventricle
lungs
Pulmonary vein oxygenated blood
lungs
left atrium
Aorta oxygenated blood
left ventricle
body
Coronary arteries oxygenated blood
aorta
the heart muscle itself
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The structure of the heart drawn as if you are looking at someone facing you — so their right side is on your left right atrium left atrium right ventricle left ventricle valves vena cava brings deoxygenated blood back from the body pulmonary artery carries deoxygenated blood to the lungs aorta carries oxygenated blood to the body pulmonary vein brings oxygenated blood back from the lungs the left ventricle has a much thicker muscular wall, because it pumps blood all the way round the body — the right one only pumps to the lungs coronary arteries run over the outside and supply the heart muscle itself with oxygen septum — keeps oxygenated and deoxygenated blood apart Deoxygenated blood: body → vena cava → right atrium → right ventricle → pulmonary artery → lungs. Oxygenated blood: lungs → pulmonary vein → left atrium → left ventricle → aorta → body. Blood passes through the heart TWICE for every circuit of the body — a double circulatory system. Valves stop the blood flowing backwards. The heart in section, with the four chambers, the four main vessels, the coronary arteries on the outside and arrows showing the direction of flow, deoxygenated blood in blue and oxygenated in red
The natural resting heart rate is controlled by a group of cells in
the right atrium that act as a pacemaker
An artificial pacemaker is an electrical device implanted to correct
an irregular heart rate
Coronary arteries supply the heart muscle with oxygen. Blood in
them is not "going to the lungs" or "around the body", and blood flows
through an artery, not "past" it
Left and right are the patient's left and right, so they appear
swapped on a diagram. The left ventricle is the thick-walled one
Two facts the exam checks directly: oxygenated blood from the lungs enters
the left atrium ; the right ventricle pumps to the lungs
The rest of this topic is in the full Exam Guide The complete AQA GCSE Biology guide — every topic, exam checklist and common mistake — is coming soon. Until then, the first topic in every unit is free to read.
In the full topic
• The heart• The lungs• Blood vesselsRead the free biology topics →