ObjectiveTo determine whether treatment of borderline hypertension reverses the cardiac 'amplifier' effect associated with increased left ventricular mass.DesignRandomized, double-blind, placebo-controlled trial involving treatment for 6 months.SettingAmbulant outpatients in a teaching hospital.ParticipantsRecruited by local doctor referral or worksite screening. Average of two readings of entry blood pressures taken 1 week apart 140–160 mmHg (systolic) or 90–95 mmHg diastolic, or both. Twenty-six previously untreated males, mean±SD age 33±9.2 years with mean±SD blood pressure 138±7.4/ 90 7.0 mmHg entered and completed the study.InterventionsTwelve subjects received captopril, average dose 72 mg/day for 24 weeks, the remainder receiving placebo.Main outcome measures: Echocardiographic left ventricular dimensions, mass and transmitral Doppler flow, as well as office, ambulatory and exercise blood pressure.ResultsIn the captopril group blood pressure was reduced significantly. Left ventricular mass decreased significantly from 205 to 195 g at 8 weeks and to 202 g at 24 weeks, returning to 232g 4 weeks after treatment. Interventricular septum thickness fell significantly at 24 weeks. Doppler parameters did not alter. Baseline 8-h ambulatory blood pressure did not change with treatment. The reduction in peak exercise systolic blood pressure in the captopril group was not different from the change in the placebo group.ConclusionBlood pressure can be effectively lowered using captopril in young subjects with borderline hypertension. Treatment is well tolerated and leads to regression of left ventricular wall thickness and mass, suggesting that treatment of blood pressure elevations may be advisable at lower levels than currently recommended.