William Harvey

The veins are the vessels which return the blood from all parts of the body to the heart.

The circulation of the blood is the cause of the pulse.

The heart is the principle of life in all animals.

The blood is the vital spirit.

The heart is a muscle of a peculiar character, the only one of its kind.

The left ventricle is thicker and stronger than the right, because it has to drive the blood through the whole body.

The right ventricle is thinner, because it only sends the blood through the lungs.

The valves of the heart prevent the blood from flowing back.

The circulation of the blood is a fact which can be clearly demonstrated.

I have observed that the blood passes through the lungs and heart by the force of the ventricles.