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.
The heart's pumping cycle has 2 phases - the filling-with-blood phase and the forcing-blood-out phase: 1  The filling phase happens when the heart muscle relaxes, allowing blood to enter and fill it - called diastole (pronounced die ass tuh lee). The left ventricle fills up with blood.