radioisotope or radionuclide scanning A test in which a radioactive substance (isotope) is injected and tracked by a gamma camera (scintillation camera).
rales Chest sounds that can be heard with a stethoscope when a person with excessive lung fluid (pulmonary edema) breathes. Caused by air passing through the fluid.
Raynaud’s disease A circulatory disorder characterized by episodes of reduced circulation to the fingers and toes. Small vessels contract suddenly in response to cold or emotional upset, cutting off the blood supply.
Raynaud’s phenomenon A term used when the symptoms of Raynaud’s disease are secondary to another condition.
red blood cells (erythrocytes) Disk-shaped blood cells whose primary function is to carry oxygen. Hemoglobin, the red pigment contained in red blood cells, enables the cells to pick up oxygen molecules from the lungs.
regurgitation In heart disease, the backflow of blood through a valve that has not closed properly (insufficiency).
renin An enzyme that is secreted mainly by the kidney and is important in regulating blood pressure.
restenosis Recurrent narrowing or blockage of a blood vessel after treatment such as balloon angioplasty.
restrictive cardiomyopathy A heart muscle disease that results in increased stiffness of the heart, causing it to have difficulty filling adequately.
rheumatic fever A childhood disease that can damage the heart, joints, and other organs. It usually develops
after a strep throat infection, and is now uncommon in the United States thanks to early treatment of strep infections.
risk factor A condition or behavior that increases the likelihood of a disease or injury. Major cardiovascular risk factors include high blood pressure or elevated blood cholesterol levels and a history of smoking. A family history of early heart attacks, diabetes, a sedentary existence, male sex, and age also increase the risk.
rubella A viral infection, also called German measles, that can cause congenital heart disease and other defects in infants born to women who contracted the disease during pregnancy.