What causes blood to flow through the heart?

Blood flows through our heart because muscles on the right and left side of the heart pump the blood in a specific pattern.

The process by which blood travels through the heart:

Right Side:

1) Blood enters the heart through two large veins. They are the Inferior vena cava and the Superior vena cava. They both allow oxygen-poor blood to enter the right atrium of the heart. Blood from below the diaphragm enters the heart via the inferior vena cava, and blood from above the diaphragm enters the heart via the superior vena cava.

2) Now, as the right atrium contracts, blood flows from the right atrium into the right ventricle through the open tricuspid valve.

3) When the ventricle is full, the tricuspid valve shuts. This prevents blood from flowing backward into the right atrium while the ventricle contracts.

4) As the ventricle contracts blood leaves the heart through the pulmonic valve and flows into the pulmonary artery and to the lungs where it is oxygenated.

Left Side:

1) The pulmonary vein empties oxygen-rich blood from the lungs into the left atrium of the heart.

2) As the atrium contracts, blood flows from the left atrium into the left ventricle through the open mitral valve.

3) When the ventricle is full, the mitral valve shuts. This prevents blood from flowing backward into the left atrium while the ventricle contracts.

4) As the ventricle contracts blood leaves the heart through the aortic valve and flows into the aorta and to the body.

Blood will eventually make a full cycle through the body and return through one of the two vena cava.