1. Because antiadrenergic therapy of hypertension may precipitate borderline cardiac compensation into failure, a method for detecting early cardiac insufficiency appeared desirable.
2. Eight out of thirty primary hypertensive patients were considered to be in incipient failure on the basis of the magnitude of the changes in left ventricular mean rates of systolic ejection and isovolumic pressure development after acute digitalization.
3. Antiadrenergic therapy precipitated these patients into overt failure, but did not affect cardiac performance in the others.
4. Left ventricular response to digitalis seems a reliable test in estimating cardiac reserve and in predicting the likelihood of decompensation after antiadrenergic treatment of hypertension.