Isovolumic systole is a period of very high intraventricular pressure, which is closely related to myocardial contractility, and to the pressures within the aorta and pulmonary arteries. During isovolumic systole, the valves between the atria and the ventricles, the mitral and tricuspid valves, are closed, as are the pulmonary valve between the right ventricle and the pulmonary artery and the aortic valve between the left ventricle and the aorta, making the right and left ventricles a closed chamber. Although the ventricles are contracting at this time and the ventricular pressure increases, the ventricles are not able to eject blood, and the ventricular volume is unchanged, so it is called isovolumic systole. At the end of isovolumic systole, when the pressure within the ventricle is greater than the pressure within the pulmonary artery and aorta, the aortic and pulmonary valves will open, the ventricle will begin to eject blood, and the ventricular volume will begin to decrease.