The left ventricle is the thickest and most powerful chamber of the heart, responsible for pumping oxygenated blood into the systemic circulation against high pressure. It forms the apex of the heart and the majority of its left border.
Location and External Features
The left ventricle is located posteriorly, inferiorly, and to the left of the right ventricle. It forms:
- The apex of the heart (at the fifth intercostal space, midclavicular line)
- The majority of the left border
- The diaphragmatic surface (inferior surface)
Shape: The left ventricle has a conical shape with a circular cross-section. This shape is optimized for pressure generation.
Wall Thickness: The left ventricular wall is the thickest cardiac structure:
- At end-diastole: 12-15 mm
- In athletes: may reach 15-17 mm (physiologic hypertrophy)
The thickness reflects the high pressure (120 mmHg systolic) required for systemic circulation.
Internal Anatomy
Ventricular Cavity
The left ventricular cavity is conical in shape and divided into inflow and outflow regions:
Inflow Tract: Extends from the mitral valve to the apex. The walls are lined with trabeculae carneae, which are finer and more numerous than in the right ventricle.
Outflow Tract (Aortic Vestibule): A smooth-walled region leading to the aortic valve. The outflow tract is located anterior and medial to the mitral valve. Its posterior wall is formed by the anterior mitral valve leaflet.
Papillary Muscles
The left ventricle contains two major papillary muscle groups:
Anterolateral Papillary Muscle: Arises from the anterior and lateral ventricular wall. It receives dual blood supply from the LAD and circumflex arteries.
Posteromedial Papillary Muscle: Arises from the inferior and septal wall. It is supplied by the PDA (right dominant circulation), making it more vulnerable to ischemic dysfunction.
Each papillary muscle sends chordae tendineae to both mitral valve leaflets.
Trabeculae Carneae
The inner surface of the left ventricle has a complex network of muscular ridges. These are more delicate than those in the right ventricle and include:
- True trabeculae: Attached at both ends
- False trabeculae: May contain Purkinje fibers
- Papillary muscles: Attached at one end to the wall, the other to chordae tendineae
Interventricular Septum
The left side of the interventricular septum forms the medial wall of the left ventricle. It is thicker than the right side and has a smooth surface. The septum is supplied by septal perforator branches of the LAD artery.
Segmental Anatomy
The left ventricle is divided into segments for wall motion analysis (commonly using the 17-segment model):
Basal Segments (6): Anterior, anteroseptal, inferoseptal, inferior, inferolateral, anterolateral
Mid Segments (6): Same six regions at the mid-ventricular level
Apical Segments (4): Anterior, septal, inferior, lateral
Apex (1): The true tip of the ventricle
This segmentation is used in echocardiography and nuclear imaging to localize wall motion abnormalities.
Function
The left ventricle functions as a pressure pump:
- Systolic pressure: 100-140 mmHg
- End-diastolic volume: 100-130 mL
- Stroke volume: 60-80 mL
- Ejection fraction: 55-70% (most common measure of systolic function)
- Cardiac output: 4-8 L/min
Left Ventricular Pressure-Volume Loop
The PV loop demonstrates the phases of the cardiac cycle:
- Isovolumetric contraction (mitral valve closes, aortic valve still closed)
- Ejection (aortic valve opens, blood ejected)
- Isovolumetric relaxation (aortic valve closes, mitral valve still closed)
- Filling (mitral valve opens, passive and active filling)
Changes in the PV loop reflect alterations in preload, afterload, and contractility.
Clinical Significance
Left Ventricular Hypertrophy (LVH)
Thickening of the left ventricular wall, commonly due to hypertension, aortic stenosis, or hypertrophic cardiomyopathy.
ECG findings: Increased QRS voltage, left axis deviation, ST-T changes. Can be diagnosed by echocardiography (wall thickness > 12 mm).
Left Ventricular Failure
When the left ventricle fails as a pump, blood backs up into the pulmonary circulation, causing pulmonary congestion and edema. Symptoms include dyspnea, orthopnea, and paroxysmal nocturnal dyspnea.
Left Ventricular Aneurysm
A localized dilation of the left ventricular wall, most commonly following an anterior myocardial infarction. Can cause heart failure, arrhythmias, and thromboembolism.
Regional Wall Motion Abnormalities
Areas of the left ventricle that do not contract normally, typically due to coronary artery disease. Echocardiography can detect hypokinesis, akinesis, or dyskinesis of specific segments.