The confused state of the literature respecting gallop rhythm, the relatively long discussions and the relatively infrequent clinical reports are the occasion for the presentation of this series of 100 cases. In the first place, the condition has been called by a number of names: first, "bruit de rappel" by Bouillaud in 1835; later, in 1875, "bruit de galop" by Potain; later still, "bruit de trot," and by the English "canter rhythm." A strict separation of these different terms, as requested by Bard, is impossible, the types of gallop rhythm merging one into the other and the terms actually designating the same general phenomenon. Gallop rhythm is the expression that has survived, and its general and common adoption indicates its usefulness, even though by strict definition it does not fit all cases. A list of the more important references in the literature to gallop rhythm appears at the end of