Left atrium

Function

The left atrium is the most posterior chamber, resting against the esophagus — a relationship exploited by transesophageal echocardiography. Four pulmonary veins deliver freshly oxygenated blood into its smooth-walled cavity, the highest-pressure atrium at 6–12 mmHg.

It is a critical reservoir: during diastole it tops up the left ventricle with the final 20% 'atrial kick' that heart-failure patients in atrial fibrillation must learn to live without. Its appendage's pectinate ridges are the classic nesting place for thrombus in AF.

Blood supply

Left circumflex coronary artery.

Nerve supply

Autonomic cardiac nerves; Bachmann's bundle delivers atrial conduction from the right atrium.

Clinical relevance

Mitral stenosis

Rheumatic scarring of the mitral valve backs pressure into this chamber — dilation, pulmonary congestion and atrial fibrillation in sequence.

Left atrial appendage thrombus

In atrial fibrillation, blood stagnates in the appendage; dislodged clot embolises to cause stroke.

Related conditions

• Atrial fibrillation
• Mitral valve regurgitation