HOW DOES THE BLOOD MOVE THROUGH THE HEART? (Looking at the left side)

1. Blood enters the left atrium from the pulmonary vein. As the atrium fills, its pressure increases
2. The increase in pressure causes the bicuspid (atrioventricular) valve to open and blood begins to trickle through to the ventricle.
3. The atrium enters systole (it contracts), and all the blood is pushed through into the ventricle.
4. The ventricle contracts, increasing the pressure. Pressure is now higher in the ventricle than in the atrium and so the atrioventricular valve snaps shut to prevent back-flow into the atrium.
5. Pressure is now higher in the ventricle than in the aorta, and so the semi-lunar valve opens and the contraction forces blood into the artery.
6. The atrium and the ventricle enter diastole (they relax). The pressure is now higher in the aorta than in the ventricle, so the semi-lunar valve snaps shut to prevent the blood from flowing back into the ventricle.
7. The atrium begins to fill again from the pulmonary vein. Pressure in the atrium increases and the atrioventricular valve opens to begin the cycle again.

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Process of the Heart's contraction and the passage of blood through the left side of the heart