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 valve(s) does not close completely, causing the blood to flow backward through the valve. The heart is forced to pump more blood on the next beat, making it work harder. Stenosis (or narrowing of the valve). The valve(s) opening becomes narrowed, limiting the flow of blood out of the ventricles or atria.