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Thrombus (blood clot, clot): A solid mass formed by blood clotting in a blood vessel or in the heart. Blood clots consist of a mesh of protein called fibrin, in which blood cells are captured.

The main risk of a thrombus is occluding a blood vessel and thereby reducing or interrupting blood flow in this vessel.

The negative influence of a thrombus may be manifested at the site where it was formed or at a remote site, where it arrives as embolus.

An example of a condition, in which thrombus causes local damage is Myocardial Infarction. Most Myocardial Infarctions occur through a mixed mechanism of thrombus occurring upon a lipid plaque (Atherosclerosis) which together can totally occlude an artery and prevent blood and oxygen supply to a part of the heart nourished by this particular artery.

An example of a thrombus that has an impact on a remote site is embolism. This is an event of a thrombus formed in the heart, which is expelled during ventricular systole to the Aorta and from there it reaches with the blood stream a remote organ, such as brain or kidney, where it causes an ischemic damage.

There are special medical conditions with increased tendency to embolism. Such are for instance rhythm disorders called Atrial Fibrillation or state after valve replacement. Blood clots formed in the heart may be sent from there as thromboembolism to different body organs and cause an ischemic damage to these organs.

Therefore, patients suffering from such conditions are often treated with drugs preventing blood coagulation (sometimes called blood thinners).
Transposition of the great vessels: A congenital heart defect.

The great vessels: the Aorta and the Pulmonary artery, originate reversely from opposite ventricles, i.e. the Aorta originates from the right ventricle instead from the left one, and the Pulmonary artery originates from the left ventricle instead from the right one.

This disorder is amenable to surgical treatment.
Tricuspid regurgitation: Abnormal systolic blood flow through the Tricuspid valve, which is located between the right ventricle and the right atrium. During the systole, the Tricuspid valve should be completely closed to enable the contracting right ventricle the voiding of its blood content only into the Pulmonary artery without being returned to the right atrium. The symptoms can include edema, general weakness, tiredness etc. The treatment, depending on severity, is surgical
Tricuspid stenosis: Narrowing of the valve located between the right atrium and the right ventricle. As a result of the stenosis, there is difficulty in voiding of the right atrium into the right ventricle during diastole. On cardiac auscultation, a diastolic murmur is perceived. Symptoms reflect overload of the right atrium.

The solution of the problem is surgery.
Tricuspid valve: The valve is located between the right atrium and the right ventricle.

Its task is enabling free blood flow from the right atrium to the right ventricle, but preventing back flow in the opposite direction during the ventricular systole, when the pressure in the ventricle mounts.
Trigeminy (trigeminal rhythm): A rhythm disturbance with a repetitive pattern composed of two normal beats (originating from the sinus) followed by a premature beat originating from the ventricle or the atrium.
Triglyceride: A certain kind of lipid consisting of Glycerin bound to 3 fatty acid molecules.

High triglyceride levels indicate a tendency to increased incidence of heart diseases, especially in women.
Troponin: A protein substance, one of the cardiac markers or enzymes (as they were called earlier) assisting in the diagnosis of Myocardial Infarction.

As a general rule, enzymes are protein substances found normally in the Myocardium (heart muscle) cells.

When infarction occurs, i.e. when cells are destroyed, enzymes are released into the blood stream and their blood level increases. Therefore it is possible to use them as markers for the diagnosis of Myocardial Infarction.

Troponin levels begin to rise 6 hours after the start of infarction.

Its presence is a strong evidence of Myocardial Infarction and its blood level remains high for several weeks.
Vagus nerve: The tenth cranial nerve. It is called "Vagus" (aberrant in Latin) due to its very long path in the body.

The Vagus nerve has many branches and it innervates many organs of the body, among others the Urinary tract, the Digestive system and the heart.

It effects the heart by slowing the heart rate.

The term "Vaso-Vagal episode" relates to over- activity of the Vagus.

Such activity can cause slowing down of the heart rate and decrease of blood pressure and as a consequence fainting. Such episodes can happen as a reaction to pain, mental stress, anxiety or stimulation of other organs that are innervated by the Vagus nerve, for example during urination or bowel movement.
Valve: A structure in a blood vessel enabling blood flow in only one direction. The valves are built of a kind of pockets, which are approximated to the wall and thus blood flow is enabled as long as pressure holds the "pockets" open.

But when blood flow is attempted in the opposite, undesired, direction, the "pockets" fill with blood, close the opening and preclude such flow.
Valve regurgitation: A condition occurring when the closure of a cardiac valve is disturbed. The function of the valves is preventing blood flow in undesired direction across a pressure gradient. When the closure is partial or incomplete, blood flow in undesired direction is enabled and this condition can cause symptoms or disease. The kind of symptoms depends on the location of the valve, on its function and on the severity of its functional disturbance.
Valve stenosis: A situation, in which the opening of a cardiac valve is not complete and thereby the passage of blood through it is impaired.
Blood flow through a narrowed valve is usually manifested by a murmur, which can be heard during the phase when blood is flowing through the valve.

Clinical symptoms depend on the severity grade of the stenosis.

Usually, the cardiac compartment that must push blood through the stenosed valve is overloaded with work and the increased burden can cause structural changes of the affected compartment.

In addition, symptoms of congestion and edema may be present because of incomplete voiding.

If necessary, surgical correction is performed.
Vein: A blood vessel that normally carries oxygen depleted blood. The flow direction in veins is from the various body organs towards the heart.
Vena Cava (“The empty vein”): This large vein is composed of two parts: the inferior (lower) and superior (upper) Vena Cava. Both parts drain oxygen depleted blood from different parts of the body to the right atrium of the heart.
Ventricle: The lower heart chambers are called ventricles.

During diastole the ventricles are filled with blood emptying to them from the atria.

The right ventricle is filled from the right atrium, while blood flows through the Tricuspid valve.

The left ventricle is filled from the left atrium, while blood flows through the Mitral valve.

During the systole the ventricles pump the blood contained in them into the large vessels.

The right ventricle empties to the Pulmonary artery, from which blood is transferred to the lungs.

The left ventricle empties to the Aorta.
Ventricular fibrillation (VF): A potentially life threatening rhythm disturbance. This disorder originates in the ventricles and is caused by very rapid and unsynchronized electrical activity, causing totally ineffective contraction. The result is a steep decline of cardiac output. This dramatic decline of effective cardiac output means less blood supply to the brain with subsequent loss of consciousness and respiratory arrest.

In fact, ventricular fibrillation is cessation of the most vital processes and without treatment death is the inevitable result. Treatment consists of basic resuscitation processes, including heart massage and artificial respiration.

In addition, defibrillation must be applied for stopping the rapid and chaotic ventricular rhythm by electrical shock.

The success chances of the resuscitation are directly dependent on the early onset of such procedures. Time is absolutely critical and the more time elapses between the onset of resuscitation actions and collapse, the less are the odds for success.

Ventricular fibrillation occurs mainly as a complication of Myocardial Infarction and it is the principal cause of demise prior to hospitalization in the myocardial infarction population of patients.
Ventricular tachycardia: A dangerous rapid rhythm disorder. It originates from the ventricles and outside the normal tissue of the Sinus.

The rate can reach very high levels, even more than 200.

Symptoms such as breathing difficulties, chest pain, dizziness and others are possible.

In most cases, treatment is mandatory. It can be treated by medications or by re-establishing the normal heart rate by electrical shock.
Vestibule: See under: Atrium
Wolff-Parkinson-White Syndrome (WPW): A congenital anatomical disorder, in which an additional electrical conduction pathway connects the atrium with the ventricle. This additional pathway is known as Kent's bundle.

Due to this bypass, electrical stimuli arising from the sinus may reach the ventricle sooner than by the normal pathway; this is responsible for the other name coined for the condition: pre-excitation syndrome.

This anatomic variation exposes the patient to rapid rhythm disorders known as supraventricular tachycardia and atrial fibrillation. However, in many instances people with this anomaly are symptomless and the diagnosis is made incidentally by a specific pattern identified on ECG .

If necessary, surgical intervention can be performed (by cauterization of the superfluous bundle).

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