Complex sentence: In aortic stenosis, the opening of the aortic valve becomes narrowed or constricted (stenotic) (i.e., due to calcification) thereby increasing the pressure the left ventricle must generate to effectively move blood forward into the aorta.
Split into simpler sentences: In aortic stenosis, the opening of the aortic valve becomes narrowed or constricted (stenotic) (i.e., due to calcification). As a consequence of this stenosis, the left ventricle must generate a higher pressure with each contraction to effectively move blood forward into the aorta.