Diovan HCT Hydrochlorothiazide, HCTZ; Valsartan tablets What do valsartan-hydrochlorothiazide tablets do?VALSARTAN-HYDROCHLOROTHIAZIDE (Diovan HCT(TM)) is a combination of two drugs used to lower blood pressure. Valsartan controls high blood pressure (hypertension) by relaxing blood vessels. Hydrochlorothiazide is a diuretic. High blood pressure can damage the blood vessels of the brain, heart, and kidneys, resulting in a stroke, heart failure, or kidney failure. By lowering blood pressure, valsartan-hydrochlorothiazide can help reduce your risk of having damage to your kidneys, heart, or other organs. This medicine does not cure high blood pressure.