When the blood supply to the heart muscle or myocardium is remarkably reduced it leads to death of the muscle fibres. This condition is called heart attack or myocardial infarction.

(i) The manual method called mouth to mouth for CPR was introduced by James Elam and Peter Safar in 1956.
(ii) It is a life saving process.
(iii) It is performed under emergency conditions when persons feel difficulty in breathing and heart beats.
(iv) CPR is needed when a patient is under treatment due to drowning, electric shock or heart attack.
(v) CPR administrated from mouth practisioner to the mouth of the victim for filling of air in the lungs of victim.
(vi) This practice promotes the circulation of blood to the vital organs.
(vii) The duration of CPR is 4-6 minutes after cessation of breath to prevent brain damage or death.
(viii) Defibrillation is simultaneously done along with CPR.
(ix) Defibrillation means a brief electric shock is given to the heart to recover the function of the heart.

The type of heart in human is myogenic because the heart beat originates from the muscles of the heart. The nervous and endocrine systems work together with paracrine signals (metabolic activity) to influence the diameter of the arterioles and alter the blood flow. The neuronal control is achieved through autonomic nervous system (sympathetic and parasympathetic). Sympathetic neurons release nor-epinephrine and adrenal medulla releases epinephrine. The two hormones bind to \(\beta\) - adrenergic receptors and increase the heart rate. The parasympathetic neurons secrete acetylcholine that binds to muscarinic receptors and decreases the heart beat. Vasopressin and angiotensin II, involved in the regulation of the kidneys, results in vasoconstriction while natriuretic peptide promotes vasodilation. Vagus nerve is a parasympathetic nerve that supplies the atrium especially the SA and the AV nodes.

The primary reflex pathway for homeostatic control of mean arterial pressure is the baroreceptor reflex. The baroreceptor reflex functions every morning when you get out of bed. When you are lying flat the gravitational force is evenly distributed. When you stand up, gravity causes blood to pool in the lower extremities. The decrease in blood pressure upon standing is known as orthostatic hypotension.

1. Surface antigens are called agglutinogens.
2. They are absent in RBC of people with '0' blood group.
3. Hence no antibodies are produced against RBC - of 'O' blood group by 'A', 'B' or 'AB' types of Blood cells.
4. Therefore people with 'O' blood group are referred to as universal donors and can donate blood to people with other groups.