1. Haemodynamic and left ventricular variables were determined by M-mode echocardiography in 21 normotensive and 36 hypertensive patients during the last trimester of pregnancy.
2. Blood pressure of hypertensive patients was lowered by bed rest only, or by oxprenolol or methyldopa, but remained elevated.
3. Cardiac output was raised in the last trimester of pregnancy in both normotensive and hypertensive patients.
4. Left ventricular mass was increased in normal pregnancy, but displayed an exaggerated increase in hypertensive patients.
5. Total peripheral resistance was inappropriately elevated in hypertensive pregnancy, except in the oxprenolol-treated group.
6. There was no reduction in heart rate or cardiac output in the group treated with β-adrenoreceptor blocking agents. These factors, in combination with normal peripheral resistance, may contribute to the improvement in foetal outcome described in maternal hypertension of pregnancy treated with oxprenolol.