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Adams-Stokes syndrome: Recurrent episodes of syncope and additional neurological symptoms caused by a drastic decrease in cardiac output due to particularly low heart rate.
Adrenalin (Epinephrine): A hormone, which is excreted from the Adrenal gland. It is known as “stress” hormone, because its secretion increases during stress and exertion. It causes changes in the body, such as accelerated pulse rate, dilatation of the pupils, and increased blood flow into the muscles of the lower extremities. It is also dubbed danger hormone, and indeed the physical changes effected by it prepare the body to react in situations of threat (for example pumping more blood to the leg muscles prepares the body to flight). Used medically, the hormone serves for resuscitation, in Asthma (dilates bronchi), in surgery (constricts blood vessels and reduces bleeding) and more.
Aneurysm: Sometimes Atherosclerosis can cause weakening of the arterial walls and as time goes by, this wall can protrude in the attenuated area.

The protruding area is called aneurysm and it is exposed to more hazards than normal areas: rupture because of wall weakness, exertion of pressure on other vessels due to the unnatural protrusion and creation of blood clots in the aneurysm with the dangerous possibility of embolism (a thrombus thrown from the heart to a distant location, where it can cause damage).

Sometimes surgical intervention may be necessary.
Angina Pectoris: A condition characterized by recurrent episodes of distressing chest pain resulting from ischemia, i.e. discrepancy between oxygen consumption and oxygen supply to the heart at a given moment. The main reason for Angina Pectoris is occlusion of a Coronary artery (artery of the heart) by an Atherosclerotic plaque, but other cases are also possible, where pains are due to a spasm of a Coronary artery caused by contraction of the smooth muscle in its walls.. At early stages of the disease, the pain appears mainly after strain or excitement accompanied by pulse acceleration. In more advanced stages, pains can appear after slight efforts or even at rest.
Antiphospholipid Syndrome (APS, Hughes syndrome, sticky blood syndrome): People suffering from this syndrome expose an increased tendency to thrombosis.

Thrombi usually occur in the lower extremities, but other body regions can be involved as well.
According to one theory, this syndrome is an auto-immune disorder with impaired immune system causing an attack against the body's own tissues and organs.
It can be diagnosed by blood tests. Treatment includes anti-coagulants.
Aorta: A blood vessel of arterial type, which is the largest artery in the human body. It originates from the left ventricle of the heart and ends in the pelvis, where it divides into two femoral arteries, each of which supplies one of the lower extremities, the right and the left, respectively. Along its entire course, smaller arteries originate from the aorta, which supply oxygenated blood to all body organs.
Aortic regurgitation: A defect of the valve located at the offspring of the Aorta from the heart. As a result of this valvular defect, leakage of blood from the Aorta back to the left ventricle during the diastole takes place. In severe cases symptoms, such as shortness of breath, chest pain and enlargement of the heart, can develop. If necessary, surgical treatment is applied.
Aortic stenosis: Narrowing of the valve between the outlet of the left ventricle and the Aorta.
This is the most frequent Valvular disease. Because the stenosis makes blood flow from the left ventricle into the Aorta more difficult, the voiding of the left ventricle is impaired. This may cause symptoms of Angina Pectoris, shortness of breath during exertion and fainting. On heart auscultation, a murmur during the systole is heard, which ensues because of the compromised blood flow through the narrow valve.
Aortic valve: The Aortic valve is located at the outlet of the Aorta and delimits the Aorta from the left ventricle.

The Aortic valve enables passage of blood through it into the Aorta during systole, the phase of contraction of the left ventricle.

During diastole, when the ventricle is relaxed and the pressure in it decreases, there is risk of reverse blood flow from the Aorta (because the pressure therein is higher) into the left ventricle. The Aortic valve is here to prevent such back flow.

In instances when the valve is damaged or does not close properly, leakage into the left ventricle (regurgitation) can occur. Such leak reduces the amount of blood pumped into the Aorta on the one hand and constitutes an additional load for the left ventricle on the other hand .
Arrhythmia: Disorder in the normal heart rhythm. Any disturbance in the creation of the electrical stimulus or its conduction can cause irregular heart rate (arrhythmia). Arrhythmias can be paroxysmal and intermittent or chronic. They can originate in the upper cardiac compartments (vestibules or atria) or from the lower compartments (ventricles). Arrhythmias can be rapid or slow, without any clinical significance or life-threatening. The therapeutic approach depends on the sort, risk level, frequency of the appearance of the disturbance and its clinical consequences.
Arteriosclerosis (calcification of arteries): Sedimentation of calcium into the arterial walls. This process or condition is different from atherosclerosis.
Artery: A blood vessel that normally carries oxygen-rich blood from the heart to other body organs.

One exception is the Pulmonary artery, which, on contrary, carries oxygen-depleted blood from the right part of the heart to the lungs.

The arterial walls include, among others, smooth muscle fibers, which enable contracture and relaxation of the vessel. These muscular fibers are under control of the nervous system.
Artificial pacemaker: A device used for generating electrical signals and maintaining regular heart rhythm in patients suffering from a disturbance in electricity generation or transfer in the heart.

The need for an artificial pacemaker can be temporary and transient or chronic and permanent.

There are external pacemakers (the pulse generation takes place outside the chest), which are usually used for pre-hospitalization period.

In permanent pacemakers, the battery is implanted subcutaneously and the electrodes are implanted into the heart.
Artificial respiration: A resuscitation activity aimed at preserving the gas exchange in the lungs. It can be accomplished by various methods, beginning with mouth to mouth respiration and ending by the use of very sophisticated respiration machines.
Asystole: Finding of a flat line on ECG, meaning that electrical and mechanical activity of the heart is absent. Practically, during Asystole the electrical stimulation system of the heart does not trigger or conduct electrical stimuli, the muscle does not contract, there is a dramatic decline in cardiac output and the result is loss of consciousness, respiratory arrest and death. The treatment is defined as reanimation and consists of external cardiac massage, mechanical respiration and intravenous injections of medicines
Atheroma: A lipid sediment narrowing the lumen of an artery. It is formed as part of a disease known as Atherosclerosis.
Atherosclerosis: An arterial disease characterized by the development of lipid plaques in the inner lining of the artery. The lipid sediments are accompanied by local inflammatory processes and by accelerated division of muscle and connective tissue cells; the final result is a plaque narrowing the lumen of the arterial vessel and diminishing the amount of blood that can pass through it at any given time. The clinical effects secondary to the existence of such a plaque in an artery can range from total absence of symptoms, through an expected and gradual clinical manifestation (development of Angina Pectoris in stress situations only) and up to a violent and unexpected event of heart attack.
Atrial fibrillation: A frequent rhythm disturbance (most frequent in elderly patients) originating from the atria and resulting in ineffective atrial contractions. It can result in rapid heart rhythm.

Due to the ineffective contraction of the atria, cardiac output is reduced and this can be clinically manifested by congestive heart failure, especially in patients with a significant background heart disease.

In addition, Atrial Fibrillation harbors an increased risk of formation of thrombi in the heart.

For this reason, people with chronic or frequent paroxysmal Atrial Fibrillation are often treated with drugs preventing thrombus formation, such as Coumadin.

Atrial fibrillation can be reverted by drugs or by electrical shock (Cardioversion).
Atrio-ventricular (AV) node: A group of cells within the Myocardium serving as a relay station for electrical signals transferred from the atria to the ventricles.

The existence of these cells is helpful for the synchronous and coordinated transfer of electrical signals from the atria to the ventricles and thus for preserving effective contraction of all heart compartments.
Atrium: The upper heart compartments are called atria (vestibules).
They are separated from the ventricles by unidirectional valves.

The right atrium receives blood from the large vein system (Superior and Inferior Vena Cava) After having been collected from all body organs, this blood has low oxygen content. From the atrium it is transported through the Tricuspid valve to the right ventricle and from there, during the ventricular systole, to the Pulmonary artery for oxygenation.

The left ventricle receives oxygenated blood from the Pulmonary veins and it voids through the Mitral valve to the left ventricle and from there, during systole, to the Aorta.

The natural cardiac pacemaker, the Sinus, is located in the right atrium and from there electrical impulses are propagated to different sites in the heart.

Various conditions, such as valvular diseases, pulmonary diseases and more, can affect the atrial status.
Balloon angioplasty (coronary angioplasty, PTCA): A therapeutic procedure performed during catheterization (Coronary Angiography) aimed at dilating a Coronary artery with stenosis caused by an atherosclerotic process. The dilatation is performed by inflating a balloon and exerting pressure upon the lipid plaque in the arterial wall.

The ballooning procedure can often replace the necessity of performing bypass surgery and an open heart operation may thus be spared from many patients, although not every lipid plaque can be dilated by this method.

One of the undesired adverse events of this procedure is re-occlusion of the dilated artery after a relatively short time. To minimize the chance of re-occlusion, stents are used.
Balloon catheter, balloon-tip catheter: A catheter with a balloon at its tip used for dilating a blood vessel or a narrowed intestine or for draining the content of an organ, such as the urinary bladder.
Bigeminy: Heart rhythm characterized by intermittent appearance of one normal beat (originating from the Sinus) followed by a second beat of atrial or ventricular origin.
Block: Disturbed electrical conductance in any part of the electrical conductive system of the heart.

Causes for the appearance of a block can be temporary and transient or chronic and permanent.

The chronic condition is more frequent in old age.

The location of a block in the conductive system may be important for the clinical effect resulting thereof.

Blocks in some sites may be unnoticeable and are detected accidentally when ECG is recorded. On the other hand, blocks can cause significant slowing of the heart rate (Bradycardia), which is accompanied by symptoms.

Possible treatment modalities depend on the clinical manifestation, the duration of the disorder, its causative factor and its risk potential.
Blood lipids: See entry: Cholesterol

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