following laplace's law, the tension upon the muscle fibers in the heart wall is the pressure within the ventricle multiplied by the volume within the ventricle divided by the wall thickness (this ratio is the other factor in setting the afterload). therefore, when comparing a normal heart to a heart with a dilated left ventricle, if the aortic pressure is the same in both hearts, the dilated heart must create a greater tension to overcome the same aortic pressure to eject blood because it has a larger internal radius and volume. thus, the dilated heart has a greater total load (tension) on the myocytes, i.e., has a higher afterload. this is also true in the eccentric hypertrophy consequent to high intensity aerobic training. conversely, a concentrically hypertrophied left ventricle may have a lower afterload for a given aortic pressure. when contractility becomes impaired and the ventricle dilates, the afterload rises and limits output. this may start a vicious circle, in which cardiac output is reduced as oxygen requirements are increased.