Uncontrolled high blood pressure can cause heart muscle 'thickening', and this increases the likelihood of complications and death. The high blood pressure explains some but not all of this increase in heart size. This study will investigate the other causes, and will measure the heart muscle 'thickness' very accurately using the latest and most accurate technique called cardiac magnetic resonance imaging (MRI). The best way to treat this heart thickening remains to be determined. We hope to be able to show that by specifically targeting the cause of heart muscle thickening we can reduce its occurrence more effectively than by other standard means of blood pressure treatment