The left atrium receives oxygenated blood from the lungs through four pulmonary veins. It forms most of the base of the heart, lying at the back, and its walls are mostly smooth apart from the pectinate muscles inside the left auricle. It sits directly in front of the oesophagus, which is why it can be imaged so well from there.
| Location | Posterior surface (base) of the heart, in front of the oesophagus and descending aorta, below the tracheal bifurcation. |
|---|---|
| Parts |
|
| Nerve Supply | Cardiac plexus; Vagus nerves (parasympathetic, slows rate); Sympathetic cardiac nerves from cervical and upper thoracic (T1-T4) ganglia (raise rate and force) |
| Blood Supply | Left circumflex artery; Right coronary artery (atrial branches) |
| Venous drainage |
|
| Lymphatic drainage |
|
Acts as a reservoir for blood returning from the lungs, a conduit during early ventricular filling, and a booster pump that adds the final portion of ventricular filling. This atrial 'kick' matters most at high heart rates and in stiff ventricles.
The left atrium enlarges with mitral valve disease, hypertension and atrial fibrillation; a dilated left atrium can press on the oesophagus and widen the carinal angle. The pulmonary vein openings are the main source of triggers for atrial fibrillation, which is the basis for pulmonary vein isolation by catheter ablation. Transoesophageal echocardiography gives very clear views because the oesophagus lies right behind it.
Chaotic electrical activity in the atria that causes an irregular pulse and loss of coordinated atrial contraction. Blood can stagnate, especially in the left auricle, raising stroke risk.
The most common primary heart tumour in adults, usually attached to the interatrial septum. It can obstruct the mitral valve or shed fragments that cause embolic strokes.
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