Final answer:
The force the heart has to overcome to expel blood from the left ventricle is called systolic blood pressure, which is highest during the ventricular ejection phase of the cardiac cycle.
Step-by-step explanation:
The force that the heart has to overcome with each contraction to expel blood out of the left ventricle is the systolic blood pressure. During the ventricular ejection phase, the contraction of the ventricular muscle raises the pressure inside the ventricle to a point that is higher than that of the aorta, allowing blood to be pumped out of the heart. Systolic blood pressure is at its highest during this phase of the cardiac cycle and must be overcome by the ventricle to allow blood to exit into the systemic circulation.