1. The influence of different arterial pressures on the relationship between diastolic filling pressure and stroke volume was studied during pharmacological cardiac nerve blockade in adult, anaesthetized spontaneously hypertensive rats in comparison with matched normotensive Wistar—Kyoto rats.

2. Peak stroke volumes, obtained by rapid blood volume expansion were similar in both types of rat, despite a more than 40% higher mean arterial pressure in the spontaneously hypertensive rats.

3. When peak stroke volumes were compared in the two groups at equal ‘normotensive’ or ‘hypertensive’ arterial pressures, they were always greater in the spontaneously hypertensive rats.

4. Calculation of diastolic wall/lumen ratios indicated that the increase of maximal stroke work in the spontaneously hypertensive rats closely matched the hypertrophic increase in wall/lumen ratio of the left ventricle.

5. These results indicate that left ventricular hypertrophy in established primary hypertension is a physiological adaptation to match left ventricular performance to the raised afterload.

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