8. The participant must have a post-placebo run-in, 24-hour mean SBP by ambulatory blood pressure monitoring (ABPM) of 140-175 mm Hg inclusive, and a clinic SBP measurement of 160 to 190 mm Hg inclusive (determined by the mean of 3 sitting, trough, measurements on Day -29) to qualify for entry in to the 4 week single-blind TAK-491 40 mg monotherapy treatment period.