The following drugs are contraindicated in patients with hypertrophic obstructive cardiomyopathy: the first, ARBs or ACEI drugs, and nitrates, which dilate the peripheral vasculature and reduce cardiac afterload, worsening outflow tract obstruction and increasing the pressure step difference in the outflow tract. The second type is diuretics, because diuretics reduce the volume of blood through urination and decrease the preload of the heart, which also increases the pressure step difference in the outflow tract of patients with hypertrophic obstructive heart disease. The third type of drug, digitalis, is the traditional cardiac drugs, which increase myocardial contractility and increase systolic left ventricular pressure, which also increases the pressure step difference in the outflow tract. These drugs will clearly increase outflow tract obstruction, so they should be prohibited.