Left ventricular ejection fraction at rest and during treadmill and isometric handgrip exercise were determined in 16 patients with essential hypertension (mean age 47.4 years) before and after therapy. The untreated hypertensive patient showed a linear correlation between mean blood pressure and LVEF (r =0.62, p < 0.01). The relation of sitting, resting LVEF with systolic blood pressure was highly significant (r =0.88, p < 0.001). Prior to therapy no significant change in LVEF in response to exercise was noted. After therapy with captopril, a normal isotonic exercise response occurred consisting of a highly significant increase in ejection fraction (p < 0.0025). Subjects receiving propranolol had a fall in LVEF with isometric stress (p < 0.0025). These data suggest an increased ejection fraction in patients with essential hypertension when all other parameters of the heart are normal and an abnormal response to isotonic exercise which may be reversed with therapy.