Contractile Strength during Variable Heart Duration Is Species and Preload Dependent

Figure 1

Following a stimulus, muscle length (y-axis) is kept constant till well after peak active force development has been reached. At 150 ms after the stimulation, muscle length is quickly reduced to 90% of optimal length and thereafter restretched at 1 muscle length per second. The duration of this stretch varied resulting in successive beats with different preloads, where the preload is increased linearly with the interbeat duration.