Our heart has four valves separating the various chambers and exit points.
The mitral valve and the aortic valve are on the left side of the heart. The mitral valve separates the left atrium and left ventricle. The aortic valve separates the left ventricle and the exit to the aorta (The big vessel carrying oxygen-rich blood around the body).
The tricuspid valve and pulmonary valve are on the right side of the heart. The tricuspid valve separates the right atrium and right ventricle. The pulmonary valve separates the right ventricle and the exit to the pulmonary trunk (A vessel which branches left and right, delivering oxygen-depleted blood to the lungs to undergo oxygenation). 

The valves on the left side of the heart develop issues more commonly, as the left side is a more powerful, higher pressure system - and so, we will discuss aortic stenosis and mitral regurgitation, the most common valvular diseases. 

Aortic Stenosis
Aortic stenosis is the medical-lingo for a narrowing of the aortic valve. This means that the left ventricle has a harder obstacle to overcome in order to pump blood around the body. 

The most common cause of the valve narrowing is calcium build up on the valve leaflets as we age, making them stiff, less malleable and therefore, a poorly functioning valve. 

The aortic valve has three leaflets, that open when the ventricle contracts and close when the ventricle is filling. This makes aortic stenosis a valve opening issue, like a rusty door. 
Approximately 1 in 50 people only have two leaflets in their aortic valve, predisposing them to aortic stenosis. 

The symptoms you may experience are called the SAD triad - Syncope (Passing out), Angina (Chest pain) and Dyspnoea (Shortness of breath). 

And why is this? 

Syncope - If a lack of blood is exiting the heart, a lack of blood reaches the brain and the lights go out. Simple. Aortic stenosis can predispose you to funny rhythms such as atrial fibrillation which may contribute to the problem but let's not get too in depth!

Angina - The coronary arteries (supply the heart muscle) begin just after the aortic stenosis, and interestingly, the movement of the aortic valve back and forth helps blood to flow through them - like the sweeping of a brush. If it's not as mobile, less blood enters the coronary arteries and the heart muscle suffers, hence the chest pain. 

Dyspnoea - To bypass the stiff valve, the left ventricle has to squeeze really hard, which increases the pressure in the left ventricle itself. This means that the left atrium has to increase its pressure to supply the left ventricle. In turn, this means the pressure of the vessels in the lungs has to increase to supply the left atrium! Talk about a domino effect.
Higher lung vessel pressure reduces the efficiency of the gas exchange (swapping carbon dioxide for oxygen) - less oxygen equals more short of breath. Took a while for us to get there but again, simple!

If a doctor suspects AS, they will listen to your heart and possibly hear a characteristic murmur - a harsh sound created by the blood squeezing through the gap. They will order an echocardiogram to visualise the valve and confirm the diagnosis. 

Depending on the suspected cause/severity of the narrowing, the doctor will treat the AS in one of two ways - medications alone or surgery. Within surgery, the valve can be replaced with open heart surgery or a less invasive procedure called a TAVI may be appropriate. 

Mitral Regurgitation
The mitral valve has two leaflets. It opens when the left atrium is filling the left ventricle, and closes when the left ventricle contracts. Mitral regurgitation is a closing problem. When closed, the left ventricle squeezes and the increased pressure causes some blood to squeak through the valve back into the left atrium. Imagine the wind blowing open a door that's meant to stay closed - chilly. 

The most common cause is mitral valve prolapse - basically the fibres that anchor the leaflets to the walls become stretchy over time, allowing the valve to bend backwards into the left atrium. Other causes include a heart attack, genetics, rheumatic fever, etc. 

The symptoms of mitral regurgitation depend on the severity. If it's mild, you may feel nothing - and the issue could be picked up when your GP listens to your heart and hears a murmur (sound created by the blood leaking back through a closed valve). 

As more blood leaks in the wrong direction, back into the atrium rather than out the aorta. This means that less blood is sent all around the body, which can lead to fatigue. It can lead to increased pressure in the left atrium - which can cause irregular rhythms such as atrial fibrillation or perhaps, increase lung vessel pressure. With and increased lung vessel pressure, fluid can build up in the lungs and cause shortness of breath, especially when lying down flat. Heart failure can develop, leading to swelling in the feet (Read the heart failure section to learn more).

Similar to aortic stenosis, an echo will be done to visualise the valve to confirm the diagnosis and measure severity. The cardiologist may choose to manage this medically or surgically (which means replacing the valve).