DESPITE THEIR COMMON USE in patients

Controversy exists over the rapidity of onset of the inotropic effect of various digitalis glyco-sides. Shortening of the systolic time intervals (STI) provides a quantitative measure of the ino-tropic effect of digitalis glycosides in human subjects. Total electromechanical systole corrected for heart rate (QS2I) is the most sensitive of the STI since it combines the shortening effect of digi-talis glycosides on both the pre-ejection period and ejection time. Normal volunteer subjects were studied serially following i.v. injection of 1.6 mg cedilanid-D (C) (n = 18), 1.0 mg ouabain (0) (n = 12), 1.6 mg digoxin (D) (n = 16), and 1.6 mg digitoxin (DT) (n =9). The shortening of QS2I was corrected for the molecular weight of the digitalis glycoside. The onset of shorten-ing of the QS2I/mole proved to be exponential for each digitalis glycoside. This allowed esti-mation of the maximum shortening of QS2I/mole (A) which would occur assuming zero excre-tion, from which the time constant (tQ) of the curves could be determined. There was no significant difference in A among the digitalis glycosides. The t, were 5.8 min (0), 7.2 min (C), 23 min (D), and 56 min (DT). These t, were significantly different except for 0 and C. Thus both C and 0 have a rapid onset of activity which is significantly shorter than either D or DT. The t. for C in patients with congestive heart failure is the same as normals. This study provides a heretofore unavailable, accurate measure of the differences among commonly used glycosides. Additional Indexing Words: Digitalis Systolic time intervals Time constant Congestive heart failur