saccular aneurysm A round, protruding distention in a weak part of an artery.
saphenous vein The vein in the legs that is often removed and used to bypass a blocked vessel in coronary bypass surgery.
sarcoidosis A rare disease that can cause inflammation of the heart muscle or heart muscle dysfunction (cardiomyopathy), as well as inflammation of the lymph nodes and tissues in other parts of the body.
saturated fats Fatty acids that contain the maximum possible amount of hydrogen. They are hard at room temperature and include most animal fats as well as palm, palm kernel, and coconut oils.
semilunar valves Heart valves that are composed of cusps in the shape of a half-moon (crescent-shaped), such as the aortic and pulmonary valves.
septal defect A congenital abnormality in which there is an opening in the dividing wall (septum) between the left and right sides of the heart. This can occur between either the atria or the ventricles.
shock A condition characterized by insufficient blood supply to vital parts of the body, which deprives them of oxygen and causes them to temporarily cease functioning. If not treated immediately, shock can lead to brain damage and even death.
single photon emission computed tomography (SPECT) A diagnostic test that is a type of radionuclide scanning. It produces a three-dimensional image through the use of a camera that rotates around the subject.
sinoatrial node The natural pacemaker in the heart, consisting of a group of specialized muscle cells on the wall of the right atrium. It controls the heart’s electrical activity.
sphygmomanometer A device used to measure blood pressure. It consists of an inflatable rubber cuff, an air pump, and a column of mercury or a dial that registers air pressure. Readings are expressed in millimeters of mercury (mm Hg).
stasis Reduced or discontinued flow; for example, a slowing of the flow of blood.
stenosis Narrowing of a blood vessel, heart valve, or other bodily passage.
stents Tiny metal “scaffolds” that support tubular structures such as arteries. A stent may be used to keep a collapsed artery open until surgery can take place, it may hold a vessel open while a physician works on it, or it may provide a permanent opening in a blocked artery, placed during percutaneous transluminal coronary angioplasty (PTCA).
stethoscope The instrument used to amplify and listen to the sounds made by the heart, blood vessels, and lungs.
stroke A disruption of blood flow to the brain, usually caused by a clot or rupture of a blood vessel.
stroke volumeThe amount of blood the heart pumps out at each contraction.
subarachnoid hemorrhage Bleeding beneath the membrane covering the brain’s surface, which can compress the brain tissue.
superior vena cava The major vein that carries deoxygenated blood from the upper portion of the body (head, neck, and chest) back to the heart.
supraventricular tachycardia A too-rapid heartbeat (140 to 180 beats per minute). It can persist for several minutes to hours or days. It occurs when the tissue above the ventricles generates impulses at a faster rate than the usual pacemaker of the heart, the sinoatrial node.
sympathetic nervous system The part of the autonomic nervous system that controls heart rate, size of blood vessels, and numerous other body functions.
syncope The medical term for fainting.
systolic blood pressure The part of the blood pressure reading that corresponds to the heart’s contraction or heartbeat. This is the greater of the two numbers in a blood pressure reading.