Abdominal Aorta

The abdominal aorta is the section of the aorta located below the diaphragm.

Abdominal Aortic Aneurysm (AAA)

A dangerous "ballooning" of the body's largest artery due to a weakness in the wall of the vessel. If left untreated, it can burst and cause death.

Ablation

A procedure in which radiofrequency energy is delivered through an intracardiac catheter to effectively heat the heart tissue and render it electrically inactive. Used to treat tachyarrhythmias.

Alveolus (Pl. Alveoli)

Alveoli are tiny air sacs in the lungs that exchange oxygen and carbon dioxide with the blood carried past them in capillaries. Adults have roughly 300 million microscopic alveoli in their lungs.

Aneurysm

An aneurysm is a weakening in the muscular walls of a part of an artery which results in an enlargement or sagging of the damaged section. Aneurysms may be caused by a congenital defect, a degenerative disease, or a syphilitic infection. An aortic aneurysm may occur anywhere in the aorta. Aneurysms located in the ascending aorta or the aortic arch are frequently treated surgically. Aneurysms located in the descending aorta are usually treated medically and are only operated on if medical treatment fails. If an aneurysm ruptures, massive bleeding can result in hypotension, coma, and death.

Angina Pectoris

Symptoms experienced when the heart muscle is not receiving adequate oxygen (may include chest, arm or back pain, shortness of breath).

Angiogram

An X-ray of blood vessels filled with contrast media; a diagnostic procedure is generally referred to as an angiogram.

Angioplasty

A less-invasive treatment of the coronary arteries to open blocked arterial vessels. Also known as percutaneous transluminal coronary angioplasty (PTCA) or percutaneous coronary intervention (PCI).

Annuloaortic Ectasia

Annuloaortic ectasia is the weakening or dilation of the annulus, the ring that surrounds the aortic valve.

Annuloplasty

Annuloplasty refers to the repair of a regurgitant valve -- a valve that is loose, or torn, permitting reverse blood flow. In an annuloplasty, the diameter of the valve is carefully measured and the defect in the valve is surgically repaired. The valve is thereby secured to prevent further leakage.

Aorta

The artery through which blood leaves the left ventricle of the heart, the aorta is the main artery of the body. All other arteries in the body stem from the aorta.

Aortic Arch

The aortic arch is the section of the aorta that travels (arches) over the heart before heading to the lower body. It originates from the ascending aorta (which is directly connected to the left ventricle of the heart) and gives off the main arterial branches to the head and arms: the brachiocephalic (innominate) artery; the left common carotid artery; and the left subclavian artery. The aortic arch later becomes the descending aorta (which travels down along the spinal column). The aortic arch helps to monitor blood pressure in the body through stretch receptors located in its outer wall.

Aortic Dissection

An aortic dissection is a tear or rip in one or several layers of the wall of the aorta. An aortic dissection is not a complete tear, or rupture, of the aortic wall, which is a lethal condition. When a dissection occurs, blood flows through the tear, filling the space between the layers of the aorta and becoming trapped. An aortic dissection usually causes severe pain. Dissection in the ascending aorta or the aortic arch are generally treated surgically. Dissections in the descending aorta are only operated upon if medical treatment fails.

Aortic Regurgitation

Aortic regurgitation occurs when some blood flows back into the left ventricle of the heart from the aorta after a heart beat. Aortic regurgitation is caused by a damaged aortic valve. When open, the aortic valve allows blood to flow from the left ventricle of the heart into the aorta. When closed, the aortic valve forms a strong seal, separating the ventricle from the aorta. If the aortic valve is damaged, a reverse in the blood flow, or aortic regurgitation, may be possible. Symptoms and signs of this condition include breathlessness, angina pectoris, enlargement of the heart, and a diastolic murmur (a murmur or slight noise heard when the heart is not contracting). While mild cases may have no symptoms, in severe cases the valve may have to be either repaired or replaced surgically.

Aortic Root

The aortic root is the thick base of the aorta where the aorta connects with the aortic valve.

Aortic Stenosis

Aortic stenosis occurs when two of the three flaps that comprise the aortic valve fuse together. This fusion narrows the opening to the aorta, thus restricting the blood flow out of the left ventricle into the aorta. Symptoms and signs of this condition include breathlessness, fainting, angina pectoris, and a systolic murmur (a murmur or slight noise heard when the heart contracts). There is no good non-surgical medical treatment for severe aortic stenosis. The valve should be replaced or repaired surgically.

Aortic Valve

The aortic valve separates the left ventricle of the heart from the aorta (the main artery of the body). The aortic valve is comprised of three leaflets that, when open, permit blood to flow in only one direction - from the left ventricle into the aorta.

Aortitis

Aortitis is an inflammation of the aorta. Possible complications of aortitis include the formation of an aneurysm or other obstruction in the ascending aorta and aortic regurgitation. Pressure from the inflammation or from a reduced blood supply may cause chest pain. In severe cases the aortic valve and sections of the aorta may have to be either repaired or replaced surgically.

Aortogram

An aortogram is an X-ray examination of the aorta which is used to help to determine the extent and location of disease including aneurysms and aortic dissections. In order to take the X-rays, a radiopaque contrast medium is injected into the aorta.

Aortography

An aortography is an X-Ray examination of the aorta, using intravenous contrast dye to outline the aorta.

Arrhythmia

Any variation from a normal heartbeat. It can be an abnormality either of the rate, the regularity or site of impulse origin or the sequence of activation. A slow heart rate is a bradyarrhythmia and a fast heart rate is a tachyarrhythmia.

Arteriovenous Fistula (AVF)

An abnormal communication between an artery and a vein, usually resulting in an arteriovenous aneurysm.

Arteriovenous Malformation (AVM)

A tangle of abnormally connecting arteries and veins, usually congenital.

Artery

Arteries are the blood vessels that carry oxygen-rich blood away from the heart to the body. Artery walls have muscles that help to maintain blood pressure and pump blood through the body. The pulmonary artery from the right ventricle to the lungs is the only artery that does not carry oxygen-rich blood.

Ascending Aorta

The ascending aorta begins at the aortic valve, which connects the aorta to the left ventricle, and extends upward until transforming into aortic arch.

Asystole

Asystole is when the heart does not beat.

Atherectomy/Atherotomy

A procedure to remove plaque from the inside of a blood vessel. Most commonly, atherectomy is done in major arteries such as the coronary arteries and other major arteries that have experienced the occlusive effects of atherosclerosis.

Atheroma

Atheroma is the substance that causes clogged arteries. Fatty plaques and scar tissue can build-up on artery walls, forming an atheroma. Common causes of atheroma are a high fat diet, smoking, obesity, and/or physical inactivity. These arterial build-ups limit blood circulation and often cause thrombus (blood clots). Symptoms and signs include angina pectoris, heart attacks (cardiac arrest), and strokes. Treatments range from prevention, to drug therapy, and coronary bypass surgery.

Atherosclerosis

Atherosclerosis is the blockage of arteries from a build-up of fatty plaques on the inner artery walls (see Atheroma).

Atrial Fibrillation

An arrhythmia where the atria beat at a much higher than normal rate, with a very disorganized, chaotic pattern.

Atrial Flutter

An arrhythmia where the atria beat at a much higher than normal rate, though in a regular pattern.

Atrioventricular Bundle (Av Bundle; Bundle Of His)

The AV bundle is a group of specialized heart muscles that connects the sinoatrial node to the AV Node, travels down through the septum -- the division between the right and left sides of the heart -- and splits off into a right bundle for the right ventricle and a left bundle for the left ventricle. These specialized muscles carry the electrical stimuli which cause the heart muscle to contract. Once the AV Node receives the message to contract, it passes it on to the AV bundle which in turn transmits the message to the muscles in both ventricles.

Atrioventricular Node (Av Node)

The AV Node is a group of specialized heart muscle in the lower-middle of the right atrium that serves as an electrical relay station for the heart. The sinoatrial node sends one electrical signal telling the atrium to contract and another signal to the AV Node. The AV Node then delays the signal before sending the message to the Atrioventricular Bundle. Finally, the AV Bundle passes the signal on to both ventricles, and they contract.

Atrioventricular Septum

The atrioventricular septum is the physical wall that separates the atria from the ventricles.

Atrium (Pl. Atria)

The atria are the upper chambers of the heart that collect blood before passing it on to the larger, more muscular ventricles. Oxygen-poor blood enters the right atrium through the venae cavae. Oxygen-rich blood enters the left atrium through the pulmonary veins.

Automatic Implantable Cardiac Defibrillators, Aicd

AICDs are devices which are placed inside the body and connected to the heart. These devices sense when the heart is beating chaotically and give strong shocks to cardiovert or defibrillate it back into a healthy heart rhythm. Some AICDs also function as pacemakers, giving little shocks to treat a too slow heart rate.

Autonomic Nervous System

The autonomic nervous system controls many of those systemic functions that the mind does not consciously govern, such as the beating of the heart. The autonomic nervous system is divided into two different sub-systems, the sympathetic nervous system, and the parasympathetic nervous system. These two systems govern many of the same parts of the body, but are responsible for giving opposing signals. A sympathetic signal will speed the heart rate and heart's strength of contraction. A parasympathetic signal slows the heart rate.