These are large, multicusped valves that prevent backflow from the ventricles into the atria during systole. They are anchored to the wall of the ventricle by chordae tendinae, that prevent the valve from inverting.The chordae tendinae are attached to papillary muscrdae tendinae are known as the subvalvular apparatus. The function close. The subvalvular apparatus have no effect on the opening and closure of the valves, however. This is caused entirely by the pressure gradient across the valve.the bicuspid valve, the mitral valve gets its name from the resemblanceto a bs is why it is made of , between the right atrium and the right These are positioned on the pulmonary artery and aorta. These valves do not have chordatendinae, but are more similar to vortic ses above the pressure in the aorta, the aortic valve opens, allowing blood to exit the left ventricle into the aorta. When ventricular systole ends, pressure in the left ventricle rapidly drops. When the pressure in the left ventricle decreases, the aortic pressure forces the aortic valve to close. The closure of the aortic valve contributes the A2 component of the second heart sound.

In the human body, the heart is normally situated slightly to the left of the middle of the thorax, underneath the sternum (breastbone). It is enclosed by a sac known as the pericardium and is surrounded by the lungs. The apex is the blunt point at thbase of the heart. A stethoscope can be placed directly over the apex and count the beats. In normal adults, its mass is 250-350 g, but extremely diseased hearts can be up to 1000 g in mass. It consists of four chambers, the two upper atria (singular: atrium) and the two lower ventricles.

A septum divides the right atrium and ventricle from the left atrium and ventricle, preventing blood from passing bated unidirectional flow o blood from the atria to the ventricles.The ventricular systole consists of the contraction of the ventricles and flow of blood into the circulatory system. Again, once all the blood empties from the ventricles, the pulmonary and aortic semilunar vales close. Finally complete cardiadiastole involves relaxation of the atria and ventricles in preparation for refilling with cculating blood.Heart action and respiratory effort are absolute requirements in transpoay sustain damage after four minutes and irreversible damage after about seven minutes. The heart also rapidly loses the ability to maintain a normal rhythm. Following cardiac arrest, effective CPR enables enough oxygen to reach the brain to delay brain death, and allows the heart to remain responsive to defibrillation attempts.

CPR is commonly taught to the general public as these may be the only ones present in the crucial few minutes before emergency personnel are available. If administered properly it can save lives but when done badly or inappropriately it can interfere with life saving operations later. Sometimes CPR should not be attempted, particularly if other persons are injured and need immediate help. CPR takes a lot of effort and may keep care providers from helping others. See triage.

CPR is almost never effective if started more than 15 minutes after collapse because permanentbrain damage has probably already occurred. A notable exception is cardiac arrest occurring with exposure to very cold temperatures. A patient cannot be pronounced dead before he has been brought back to a normal temperature by appropriate means: Hypothermia seems to protect the victim by slowing down metabolic and physiologic processes, greatly decreasing the oxygen needed by tissues. There are cases where CPR, defibrillation, and advanced warming techniques have revived hypothermia victims after over 30 minutes or longer.

In respiratory arrest, when the victim still has a heartbeat (such as in drowning, choking, or drug overdose with opioids or sedatives) Rescue breathing (rather than CPR) should be used.

The function of the right side of the heart (see right heart) is to collect deoxygenated blood from the body and pump it into the lungs so that carbon dioxide can be dropped ofand oxygen picked up. this happens through a process d from the body enters the right atrium through two great vein, the superior vena cava wchdrains the pper part of the body and the inferior vena cava that drains the lor par. taks plces and the blood releases carn dioxide into the lung cavity and picks up oxygn. The oxygeated blood then flows through pulmonary veins to the left atrium. From the left atrium this newly oxygenatelood passes through the mitral valve to enter the left ventric to pump blood around the entre body, which involves exerting a considerable force to overcome the vasculposed of a lium made up of cardiac muscle. The endocardium is a further layer of flattened epithelial cells and connective tissue which lines the chambers of the heart.

take pains to discredit the contemporary chronicler Stefano Infessura's story of Innocent VIII's deathbed. In1492, as the Pope sank into a coma, te harrowing story was told that, at the uggestion of a physician, the blod of three boys was ifused into the dying pontiff's veins. They were ten years old, and had been promised a ducat each. All three died. Historians of medicine note this event as thefirst reported historical attempt at a blood transfusion. syringe for drect interhuman blood transfusionWith Harvey's discovery of he circulation h successful experiments , and Denys was accused of murderion was performed on March 27, 19ion institute was set up by Alexander Bogdanov (whowour nee or other. These otitis B and hepatitis C and others)can be passed from the donor t reciient. Tis has led to strict human blood transfusion standards ndeveloped countries, uch as Standards include screening for potential risk factors and health problems including determining donor hemoglobin level, and answering a set of standard oral and written questions, as well as testing donated units for these infections. The lack of such standards in placs like rural China, where desperate villagers donated plasma for money and had others' red blood cells reinjected, has produced entire villages infected with AIDS.