This paper reviews the cardiovascular effects of an aqueous extract of animal heart, which was in clinical development in the early 1950s. The aqueous extract reversed the negative inotropic effects of hypoxia in the frog heart preparation. In extensive observational clinical trials between 1950 and 1975, beneficial effects were reported on reducing cardiac arrhythmias, improving effort in angina pectoris, as well as improving heart failure. The majority of clinical publications came from Germany, Switzerland and Austria. Jackson and Temple identified tyramine as the main constituent in the aqueous extract. While the hemodynamic effects of tyramine in humans are well characterized, the relationship to its clinical efficacy remains speculative.