starling experimented on intact mammalian hearts, such as from dogs, to understand why variations in arterial pressure, heart rate, and temperature do not affect the relatively constant cardiac output. more than 30 years before the development of the sliding filament model of muscle contraction and the understanding of the relationship between active tension and sarcomere length, starling hypothesized in 1914, "the mechanical energy set free in the passage from the resting to the active state is a function of the length of the fiber." starling used a volume-pressure diagram to construct a length-tension diagram from his data. starling's data and associated diagrams, provided evidence that the length of the muscle fibers, and resulting tension, altered the systolic pressure.