ERA. 1  baseball, baseball game - a ball game played with a bat and ball between two teams of nine players; teams take turns at bat trying to score runs; he played baseball in high school; there was a baseball game on every empty lot; there was a desire for National League ball in the area; play ball!.
The contraction of the heart muscle starts in the two atria, which push the blood into the ventricles. Then the walls of the ventricles squeeze together and force the blood out into the arteries: the aorta to the body and the pulmonary artery to the lungs.
Veins branch at their beginnings into tiny venules which join capillaries.  Veins have valves which stop the blood from flowing backward. Compared to the arteries, pressure in the veins is very low. The blood is being pushed through the arteries as the heart squeezes the blood out. This is not true for the veins. Blood is pushed through the veins when body muscles contract and squeeze the veins.