“…21 In 1879, Charles Smart Roy, one of Foster's pupils, described the dependence of the work of the frog heart on diastolic volume (Figure 1). His report, published the follow-ing year, 22 acknowledges a "debt of gratitude" to Kronecker, one of Ludwig's pupils. Roy's work showed that "at constant aortic pressure and heart rate, the [work of the heart] is capable of being varied within wide limits by variations in the venous pressure," and concluded that "we must look to the quantity of blood arriving at the heart as the predominating factor in regulating the work done."…”