Q. What do you mean by Contractility?
Heart being a muscular pump the ability to eject blood depends on the ability to contract. Another factor is the resistance in the vascular bed through which the heart must pump. The resistance in the lungs is so low in the healthy subject that it plays very little role as a limiting factor in exercise.
Resistance is the product of blood flow multiplied by the blood pressure. When the heart pumps more blood, the cardiac output increases more than the resistance drops therefore, there is a modest increase in systolic blood pressure during exercise in healthy individuals.