Atrioventricular valves are the two one-way gates inside your heart that sit between the upper chambers (atria) and the lower chambers (ventricles), opening to let blood through and snapping shut to prevent it from flowing backward. You have two of them: the mitral valve on the left side and the tricuspid valve on the right. Together they open and close more than 100,000 times a day, and the way they accomplish this is more intricate than most people realize, involving not just flaps of tissue but an entire anchoring system of cords and muscles working in concert with blood flow patterns.
Basic Anatomy of the Two Valves
Each atrioventricular valve is built from several components that work as a unit. There is a ring-shaped frame called the annulus, leaflets (the thin flaps that swing open and closed), and beneath those leaflets a support system made of tendinous cords (chordae tendineae) and papillary muscles that protrude from the ventricle wall.1The Annals of Thoracic Surgery. Development of the Atrioventricular Valves: Morphological and Clinicomorphological Correlations Think of the leaflets as a parachute and the chordae tendineae as the parachute’s cords, with the papillary muscles as the harness that anchors everything to the ventricle floor.
The mitral valve, on the left, has two leaflets (which is why it is also called the bicuspid valve). The tricuspid valve, on the right, has three. This difference in leaflet count is not cosmetic: the left side of the heart generates much higher pressures because it pumps blood to the entire body, while the right side only pushes blood to the lungs. The two-leaflet design of the mitral valve, with its thicker tissue and sturdier cord attachments, is adapted to handle that workload.
How Opening and Closing Actually Work
The common picture is that these valves open passively when blood pushes through, then slam shut when the ventricle contracts. That is roughly right, but the timing is subtler. Research using models of the left ventricle and mitral valve showed that the mitral valve achieves most of its closure during the filling phase (diastole), before the ventricle even begins to contract. A swirling vortex of blood that forms behind the leaflets during filling, combined with the slowing of inflow, pushes the leaflets toward each other well before systole finishes the job.2Cardiovascular Research. Fluid mechanics of a model mitral valve and left ventricle The final contraction of the ventricle then seals the leaflets completely and forces blood out through the aortic or pulmonary valve instead of back up into the atrium.
This means the valve is not simply a passive flap that responds to pressure. The geometry of the ventricle, the speed at which blood flows in, and the vortex that naturally forms during filling all contribute to a highly efficient closing mechanism. When these dynamics are disrupted, as can happen when the ventricle enlarges or changes shape, valve function suffers even if the valve tissue itself is healthy.
What the Chordae Tendineae Actually Do
The cord-like chordae tendineae are often described as simple tethers that keep the leaflets from flipping inside out. That is true of one type, but the system is more specialized than it sounds. Chordae come in different orders. The first-order (primary) chordae attach directly to the free edge of the leaflet, and their main job is preventing prolapse, the condition where a leaflet billows too far into the atrium. These primary cords are stiffer and less stretchy. The second-order chordae attach farther back on the leaflet’s underside and play a different role: they help maintain the shape and pumping efficiency of the ventricle itself.3PubMed Central. Morphological Study of Chordae Tendinae in Human Cadaveric Hearts These second-order cords are more elastic and larger, mediating the mechanical connection between the valve and the ventricle wall.
This distinction matters clinically. If a primary chord ruptures, the leaflet it supports can flop backward into the atrium, causing immediate regurgitation (backward leaking). If a second-order chord is lost, the leak may not happen right away, but the ventricle’s ability to contract efficiently declines.4PubMed Central. Mechanics and Microstructure of the Atrioventricular Heart Valve Chordae Tendineae: A Review Surgeons need to understand these roles when deciding how to repair a faulty valve, because simply reattaching any cord is not the same as reattaching the right kind of cord in the right place.
Mitral Versus Tricuspid Differences
People tend to think of the mitral and tricuspid valves as mirror images. They are not. Beyond the leaflet count, the tissue itself is structurally different. Studies comparing the chordae of the two valves under electron microscopy found that tricuspid valve chordae are less extensible (less stretchy) than mitral chordae of the same size. The collagen bundles in tricuspid chordae are straighter and more tightly packed, while mitral chordae are more elastic.5The Japanese Journal of Physiology. Mechanical Properties and Ultrastructure of Normal Human Tricuspid Valve Chordae Tendineae
This seems counterintuitive at first: the left-side valve, which faces higher pressures, has the more elastic cords. But it makes sense when you consider the different mechanical demands. The left ventricle contracts more forcefully and changes shape more dramatically during each beat. Its valve’s support structures need to absorb and distribute more dynamic force, so flexibility is an advantage. The right ventricle operates at lower pressure and deforms less, so its cords can afford to be stiffer. These fine structural differences are thought to reflect the different mechanical stresses each valve endures over a lifetime.
What Heart Sounds Tell You About AV Valves
When a doctor listens to your heart with a stethoscope, the first sound they hear (the “lub” in “lub-dub”) is generated largely by the atrioventricular valves. Closure of the mitral and tricuspid valves at the start of ventricular contraction causes a sudden stop in the backward flow of blood, and that abrupt halt sets the blood column and surrounding structures vibrating.6PubMed Central. Hemodynamics-driven mathematical model of first and second heart sound generation The first heart sound has two components: the mitral component (M1) and the tricuspid component (T1). In most people, M1 comes slightly before T1 because the left ventricle contracts a fraction of a second earlier.
The loudness and pitch of this sound depend on how fast pressure is building in the ventricle at the moment the valve snaps shut. Computational modeling has shown that the sound’s intensity rises in a nearly straight-line relationship with the rate of pressure increase, while the peak frequency shifts in a more complex way depending on the pressure across the valve at the moment of closure.7PubMed. Haemodynamic determinants of the mitral valve closure sound: a finite element study This is why certain conditions change what the stethoscope picks up. A stiff valve, for instance, produces a louder snap. A leaking valve may produce a whooshing murmur that extends beyond the normal sound. Experienced clinicians can often tell the difference between mitral and tricuspid abnormalities just by where on the chest the abnormal sound is loudest.
The Tissue That Keeps Valves Flexible for Decades
Heart valve leaflets are not simple membranes. They are layered structures built from a network of extracellular matrix proteins, including collagen, elastin, and proteoglycans, organized in distinct layers that allow the leaflet to flex, stretch, and snap back with each beat. Over an average human lifespan, these valves cycle roughly three billion times.8PubMed Central. Biology and Biomechanics of the Heart Valve Extracellular Matrix That is an extraordinary amount of wear, and the valves cope by continuously remodeling: resident cells called valvular interstitial cells break down old matrix and lay down new material throughout life.
When this remodeling process goes wrong, the consequences cascade. Too much collagen makes the valve stiff, restricting flow. Too much proteoglycan and too little collagen makes the leaflet floppy and prone to prolapse. The balance is maintained by signaling pathways and enzymes that, in health, keep production and breakdown in equilibrium. Understanding this active maintenance helps explain why valve disease is not simply about mechanical wear: it is as much a biological process as an engineering one.
Mitral Valve Prolapse
Mitral valve prolapse is one of the most common valve abnormalities, defined as one or both mitral leaflets bulging abnormally into the left atrium during the ventricle’s contraction. In most cases it causes no symptoms and is discovered incidentally, but it can progress to significant regurgitation and, in rare cases, heart failure or dangerous rhythm disturbances.9PubMed. Mitral valve prolapse
The underlying problem in many cases is myxomatous degeneration, a condition where the normal layered structure of the leaflet breaks down. Enzymes that digest the extracellular matrix become overactive, the balance between collagen and proteoglycans shifts, and the leaflet becomes thickened and floppy. Research has identified overactive signaling through a growth-factor pathway (TGF-β) as a key driver, and blocking that pathway with certain blood-pressure medications has shown promise in slowing progression in experimental settings.10PubMed Central. Biology of mitral valve prolapse: from general mechanisms to advanced molecular patterns-a narrative review This is still an active area of research, but it represents one of the first times doctors have had a plausible drug target for a condition traditionally treated only by watching and waiting or eventually operating.
Rheumatic Heart Disease and the Mitral Valve
In much of the world, the leading cause of atrioventricular valve damage is not age-related degeneration but rheumatic heart disease. It starts with a strep throat infection that triggers an immune overreaction. The immune system, confused by molecular similarities between the strep bacterium and heart tissue, attacks the valve. What makes rheumatic heart disease especially insidious is that even after the acute inflammation resolves, the valve continues to deteriorate. Mechanical stress from altered blood flow keeps activating cells within the valve tissue, driving ongoing scarring and thickening.11PubMed Central. Chronic Mitral Valve Fibrosis in Rheumatic Heart Disease: From Immune Trigger to Inflammatory and Mechanical Progression
Histological examination of diseased rheumatic mitral valves reveals a complex mix of changes. In one study from a cardiac institute in Tanzania, over 70% of surgically removed valves showed fibrosis, about two-thirds showed signs of edema and fibrinoid degeneration, and more than half had calcification.12Cardiovascular Pathology. Histopathological evaluation of chronic rheumatic mitral valve stenosis The damage was widespread and did not follow a neat pattern, which helps explain why rheumatic valves are notoriously difficult to repair and often need to be replaced entirely.
How Doctors Assess These Valves
Echocardiography (ultrasound of the heart) remains the standard first-line tool for evaluating atrioventricular valves. It can show leaflet motion, measure how well the valve opens and closes, and estimate the severity of any leakage. But ultrasound has limitations, particularly with the tricuspid valve, which sits farther from the chest wall and can be harder to image clearly.
Cardiac MRI is increasingly used as a complement. Advanced three-dimensional velocity-encoded MRI can track blood flow through both valves with high accuracy, and studies have found that it correlates strongly with reference measurements, outperforming older two-dimensional MRI techniques that tended to overestimate flow volumes.13PubMed. Mitral valve and tricuspid valve blood flow: accurate quantification with 3D velocity-encoded MR imaging with retrospective valve tracking Newer deep-learning-based approaches that automatically track the valve’s position as it moves through the cardiac cycle are showing even more consistent results for the tricky tricuspid side.14PubMed Central. Tricuspid valve flow measurement using a deep learning framework for automated valve-tracking 2D phase-contrast
One area where diagnostic precision still falls short is grading the severity of tricuspid regurgitation. A prospective comparison found only fair agreement between echocardiography and cardiac MRI when classifying the severity of tricuspid leakage: just about a third of patients graded as having severe regurgitation on echo met the same threshold on MRI.15PubMed Central. Prospective Quantification of Tricuspid Regurgitation With Echocardiography vs 4D Flow Cardiac Magnetic Resonance This discrepancy has real consequences because decisions about whether to intervene surgically often hinge on how severe the leakage is judged to be.
Repairing and Replacing Atrioventricular Valves
When an atrioventricular valve fails badly enough to require intervention, surgeons generally prefer repair over replacement. Keeping the patient’s own valve preserves the connection between the leaflets and the ventricle, which, as discussed earlier, matters for the ventricle’s pumping efficiency. Classical repair techniques involved cutting out the section of leaflet that was prolapsing, but since the 1980s surgeons have increasingly turned to artificial chords made of expanded polytetrafluoroethylene (ePTFE) sutures to replace ruptured or stretched chordae tendineae.16PubMed Central. Mitral valve repair with artificial chords: Tips and tricks These synthetic cords are durable and avoid the need to cut away valve tissue, preserving more of the leaflet’s surface area for sealing.
For patients too frail for open-heart surgery, transcatheter (catheter-based) approaches have changed the landscape. The most established device is the MitraClip, which is threaded through a vein and guided to the mitral valve, where it clips the leaflets together at the point of leakage. A landmark trial in patients with heart failure and significant mitral regurgitation found that adding this device to standard drug therapy roughly halved the rate of heart failure hospitalizations and reduced death from any cause within two years compared to medication alone.17PubMed. Transcatheter Mitral-Valve Repair in Patients with Heart Failure Beyond edge-to-edge clipping, newer catheter-based strategies are in development, including devices that tighten the annulus from inside the coronary sinus and systems that replace ruptured chords without open surgery.18PubMed Central. Transcatheter mitral valve repair/replacement for primary mitral regurgitation Full transcatheter valve replacement, still less mature for the mitral position than for the aortic valve, is also progressing for cases where repair is not feasible.
How These Valves Formed During Development
The atrioventricular valves do not start out as the delicate leaflets you see in an adult heart. Early in embryonic development, the region between the atria and ventricles is filled with thick pads of tissue called endocardial cushions. The cells that populate these cushions originate from the inner lining of the heart tube and undergo a dramatic identity shift: they transform from flat, sheet-like endocardial cells into mobile, tissue-building mesenchymal cells.19PubMed. Molecular regulation of atrioventricular valvuloseptal morphogenesis This transformation is tightly regulated by molecular signals, and errors in the process can produce congenital valve defects.
The cushions eventually thin and remodel into the mature leaflets, chordae, and papillary muscles. The same molecular pathways that drive this embryonic formation, particularly TGF-β signaling, also show up in valve disease later in life, which is one reason researchers studying adult valve disorders pay close attention to developmental biology.
An Evolutionary Window Into Valve Design
Humans are not the only animals with atrioventricular valves, and comparing hearts across species reveals how these structures evolved. In reptiles like lizards and snakes, the atrioventricular region develops from cushion tissue arranged in a pattern strikingly similar to what is seen in mammals during embryonic life, with a large cushion on top and one on the bottom. These cushions correspond to specific leaflets: the upper cushion is thought to be the evolutionary ancestor of the septal leaflet of the mammalian tricuspid valve and the aortic leaflet of the mitral valve.20PLoS ONE. Development of the Hearts of Lizards and Snakes and Perspectives to Cardiac Evolution Some reptilian hearts also develop additional side cushions that resemble, at least in position, the arrangement seen in amphibians and fish, which often have a four-cusped single valve rather than two separate ones.
The separation into distinct left and right valves appears to have co-evolved with the full division of the heart into four chambers, which was necessary to keep oxygen-rich and oxygen-poor blood from mixing. The two-leaflet versus three-leaflet distinction between the mitral and tricuspid valves, rather than being arbitrary, reflects the different pressures and flow patterns that emerged once the left and right circuits became fully independent. In a sense, the asymmetry of your atrioventricular valves is a record of the evolutionary pressures that shaped the mammalian circulatory system.