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.
Too thick or too stiff. The heart's ventricles can have trouble filling with blood for two main reasons. Overworked heart muscle can bulk up, like a weightlifter; this reduces the open space inside the ventricles. Alternatively, the heart muscle may stiffen and become less flexible.