Heart - A muscular organ, which, by contracting rhythmically, around 60 times a minute, keeps up the circulation of the blood. In adult mammals and birds, the heart is four-chambered, the right auricle and ventricle being completely separated from the left auricle and ventricle. The hearth receives the blood from the veins and contracts to send blood through the arteries.
 
Heart Attack - The damage that occurs to the heart when one or more of the coronary arteries become blocked.
 
Heart Block - see Atrioventricular Block
 
Heartburn - see Pyrosis
 
Hemorrhage - To bleed.
 
High Blood Pressure - see Hypertension
 
Hypercholesteremia - High levels of bad cholesterol in the blood. It causes various heart diseases including coronary artery disease. Also called hypercholesterolemia.
 
Hypertension - Blood pressure that is consistently (more than 6 months) above 140/90. Systolic blood pressure is the top number. Diastolic blood pressure is the bottom number. Hypertension may have no known cause (essential or idiopathic hypertension) or be associated with other primary diseases (secondary hypertension).
 
Hyperthyroidism - Abnormal functioning of the thyroid gland, most commonly the increase secretion of thyroid hormone.
 
Hypervolaemia - Abnormal increase in the volume of circulating fluid (plasma) in the body.
 
Hypotension - Abnormally low blood pressure, seen in shock but not necessarily indicative of it.