Not Medical Advice: The sharpest rise of ventricular pressure is during the systole - contraction phase of the cardiac cycle.
During ventricular systole, the intraventricular pressure rises and reaches above that of the aorta (80 - 120mm Hg) during the beginning of the ventricular ejection phase when the aortic semilunar valve open and blood starts flowing from the left ventricle into the aorta.
Hence, the aortic pressure starts rising along with the intraventricular pressure during the rapid ejection phase and reaches maximum (120mm Hg) at the end of the rapid ejection phase.
During the ventricular ejection phase, about 80mL of the blood is ejected by each ventricle, this is called stroke volume. The percentage of the end-diastolic volume that is ejected out with each stroke during systole (about 65%) is called ejection fraction. Thus, about 50mL of the blood in each ventricle at the end of the ventricular systole is called end-systolic volume.
Learn more about the heart as a pump; cardiac cycle, cardiac output and venous return at the Medical Physiology for Undergraduate Students.
Of interest here are 36 interesting facts about the human heart from Factretriever.com.