The part about the hippo was already there...

Ouabain is used worldwide extensively by scientists for in-vitro-studies to block the sodium pump (Na-K-ATPase). In many non rodent species, low concentrations of this substance (i.e., in the nanomolar range) provide effective stimulation of the NaK-pump. The issue in rodents is more complicated because there are different isoforms of the NaK-pump - some of which are very sensitive to ouabain while others are not. Ouabain is no longer widely used for the treatment of human heart failure. However, in France and Germany, intravenous ouabain has a long history in the treatment of heart failure, and some continue to advocate its use by mouth in angina pectoris and myocardial infarction. There is limited anecdotal evidence for improved efficacy of ouabain relative to digoxin in a small number of patients. However, no well controlled research exists that proves or disproves the efficacy this practice. A sufficiently concentrated ouabain dart can bring down a Hippopotamus. The Galápagos tortoise, however, is immune to the effects of ouabain darts.