How does the heart pump blood through the body?

Blood is pumped through the body by the heart by two different circuits, one of the circuits in the systemic circuit and the second circuit is the pulmonary circuit.

The system circuit, starts via the left atrium and passing the mitral valve down into the left ventricle. The ventricle will then contract shortly after the atria have started relaxing and followed by the closing of the atrioventricular valves, so blood does not back wash into the atrium. Pressure will becoming higher in the left ventricle allowing ventricular systole's second phase to begin by forcing blood through the aortic semilunar valve up into the aorta so blood may reach the rest of the tissues in the body. Afterwards, the ventricles will becoming diastoling (relaxing) and pressure is now higher in the aorta then it is within the ventricles and this will cause back flow of blood back down to the ventricles but the aortic semilunar valve is has shut itself so blood may not backwash back into the ventricles. During this time, blood will be slowly returning back into the left atrium by ventricular diastole second phase & atrial systole but do note that the atrioventricular valves are still closed so blood doesn't wash into the ventriculars.

Blood will travel through arteries then to arterioles and lastly to capillaries so it may begin a gas exchange of oxygenated blood to the tissues to unoxygenated blood back to the heart, via the capillaries, venules, veins then superior & inferior vena cava.

Next is the pulmonary circuit which it will return the deoxygenated blood into the right atrium via the superior/inferior vena cava down the tricuspid valve to the right ventricle and blood will be forced up into pulmonary trunk via the pulmonary semilunar valve to the pulmonary arteries via the ventricular systole (same exact process as systemic circuits.) It will then travel towards the lungs, via the ateries then arterioles and capillaries once again but this time the capillaries with run along aveoli which are air sac's of the lungs that control the gas exchange between our atmosphere's....So, as you breath out you are going to be releasing the carbon dioxide from the tissues that were collected from those veins and transported via the arteries but as you breath in. oxygen will be inhaled back into the aveoli and will now allow oxygenated blood to return it back into the pulmonary venules then to the pulmonary veins to return back to the heart so it may re-enter back into left atrium and pass the mitral valve into the left ventricle via ventricular systole and back through the aortic semilunar valve to the aorta and to the rest of the bodies tissue.