magnetic resonance imaging (MRI) A diagnostic technique that uses the response of atoms to a magnetic field to produce cross-sectional images of the body’s internal structures.
Marfan syndrome A rare inherited disease of the connective tissues that produces abnormalities in the skeleton, heart, and blood vessels.
metabolism The physical and chemical processes necessary to sustain life.
micturition The medical term for urination.
mitral insufficiency (regurgitation) Failure of the mitral valve to close properly, allowing some blood to flow back into the left atrium rather than moving forward into the left ventricle.
mitral valve The valve that controls the flow of oxygenated blood from the left atrium into the left ventricle.
mitral valve prolapse A congenital abnormality in which the leaflets, or flaps, of tissue that makeup the mitral valve are larger than normal.
monounsaturated fats : Fatty acids that are capable of absorbing more hydrogen. They are soft at room temperature and have little effect on the amount of cholesterol in the blood. Examples include olive oil and chicken fat.
multigated acquisition (MUGA) scan A radioisotope test used to measure heart function and performance.
multivessel disease Blood vessel disease in which more than one vessel (usually coronary) is blocked or otherwise impaired.
murmur See heart murmur.
muscular dystrophy An inherited childhood disease characterized by progressive muscle wasting and weakness. The disease affects male children, who inherit the defective gene from their mothers.
myocardial infarction Medical term for a heart attack, denoting damage of the heart muscle as a result of a reduction in blood flow.
myocarditis Inflammation of the heart muscle.
myocardium The heart muscle.
myxomatous degeneration A metabolic process in which valve tissue loses elasticity and becomes redundant.