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A Glossary of Heart Disease Terms


Mechanical Valve: In people who require heart valve replacement surgery, it is sometimes desirable to implant a mechanical valve. A mechanical valve is made of artificial parts and functions similarly to a normal heart valve. People who have a mechanical valve implanted must take blood thinners lifelong to prevent blood clots from forming on the mechanical valve.

Metabolic Exercise Stress Test (also called metabolic stress test): A test used to measure the performance of the heart and lungs while they are under physical stress. The test involves walking on a treadmill or pedaling a stationary bike at increasing levels of difficulty, while being closely monitored.

Minimally Invasive Heart Surgery: Minimally invasive heart surgery is a technique developed to reduce the trauma associated with open heart surgery. The smaller incision that is used may allow the patient to heal more rapidly. It also helps to reduce the pain and discomfort associated with heart surgery.

Mitral Insufficiency (mitral regurgitation): A condition where blood in the left ventricle leaks back through the mitral valve into the left atrium and can back up into the lungs. The mitral valve normally opens to allow blood to flow into the left ventricle and then closes, preventing blood from backing up into the atrium during the ventricle's contraction. This may be associated with mitral valve prolapse or can develop due to other forms of heart disease.

Mitral Stenosis: A condition where the mitral valve becomes narrowed (stenotic), preventing the easy flow of blood from the left atrium into the left ventricle.

Mitral Valve: The valve that lies between the left atrium and left ventricle (main pumping chamber of the heart). This valve allows blood to flow from the left atrium into the left ventricle and then prevents the back flow of blood into the left atrium during ventricular contraction.

Morbidity Rate: The percentage of people who have complications from a medical condition or after a procedure or treatment.

Mortality Rate: The percentage of deaths associated with a disease or medical treatment.

Multigated Acquisition Scan (MUGA scan): A nuclear scan that evaluates the pumping function of the ventricles by determining the heart's ejection fraction.

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