i was pretty good in science last time
and my english is okay too.

Ehem,
SPOILER]

well, for human's heart we have four chambers and two circulations. We call this system the double complete circulation system.

First the deoxygenated blood  enters and fills the right atrium via the vena cava. the sino-atrial node(SA node) sends signals for atrium to contract. the deoxygenated blood then enters the r. ventricle. the Artrioventricular node(AV node) then sends signals for the ventricles to contract. the ventricles contract and sent the blood out throught the pulmonary artery.
the blood goes to the lungs to be oxygenated and is sent back to the heart's left atrium. then, the atrium contracts again becaus of the SA node which we saw earlier. You should also keep in mind that there is deoxygenated blood in the right chambers. the blood then moves to the left ventricle which has thicker walls. this enables the heart to pump harder and send the blood to all parts of the body. About the purkinje fibres and Bundle of His, its the nerves in the heart that causes it to contract. a bit har to explain la. u see the gif earlier 

About the blood, as you know, we have 4 basic blood groups, as by the ABO system. The groups are: A, B, AB and O.
A type blood has the a-antigen. Think of it as an A-type sword, for lack of a better analogy.
this A type blood has the A type sword and the anti-B antibody (troops). This anti-B troops will attack only B type swords. The B type has the B type antigen (sword) And anti-A antibodies, while AB has both A and B types of antigens and NO antibodies.
when A mixes with A type, they have no problem.
however when B mixes with a patient with A blood, they clash as the the B type blood has the B antigen while the A type blood contains anti-B antibodies. This causes them to "fight".

for AB however, they dun have problem coz they dun have antibodies or troops who will fight. so they can receive blood from all. However they got both A and B antigens or swords, so they will cause problem if they go into another persons system.

for O, they have both type of antibodies or troops, but no swords. they can enter any persons body without causing harm as they dun have the swords to attack, but when any other type of blood comes in, their antibodies, or troops, will attack.  deswai they can only receive from O.

Actually, there's more to blood types, but this is all you need to know for now