afterload can also be described as the pressure that the chambers of the heart must generate to eject blood from the heart, and thus is a consequence of aortic pressure (for the left ventricle) and pulmonic pressure or pulmonary artery pressure (for the right ventricle). the pressure in the ventricles must be greater than the systemic and pulmonary pressure to open the aortic and pulmonic valves, respectively. as afterload increases, cardiac output decreases. cardiac imaging is a somewhat limited modality in defining afterload because it depends on the interpretation of volumetric data.