The left ventricular wall stress is the force acting against the myocardial cells. This is directly proportional to the left ventricular pressure and radius. Wall stress is indirectly proportional to two times the wall thickness. This was described with the Law of LaPlace which is quite important in order to understand which disease states can alter oxygen demand resulting in angina and which therapies can relieve angina:

Left ventricular wall stress = LV pressure x LV radius
                                              2  x  LV wall thickness

Left ventricular pressure increases with states that increase “afterload” of the heart including systemic hypertension and aortic valve stenosis.

Left ventricular radius increases in valvular heart disease (especially aortic regurgitation) or cardiomyopathies causing systolic heart failure.

Left ventricular wall thickness increases in chronic hypertension or aortic valve stenosis as a compensatory mechanism to decrease wall stress (inversely proportional to wall stress) thus decreasing oxygen demand (since the stress will be distributed over a larger mass). Hypertrophic obstructive cardiomyopathy (HOCM) similarly increases wall thickness. After myocardial infarction, the wall thins during remodeling which increases wall stress.