Figure 1. Prolonged action potentials increase Ca²⁺ transients and unloaded cell shortening in rat cardiac myocytes.

A, trains of eight short control APs (left) and long post-MI APs (right) were used to load the myocyte to steady-state SR Ca²⁺ load. B, Ca²⁺ transients measured from the final 9th control AP (left panel) and post-MI AP (right panel). C, unloaded cell shortening associated with the intracellular Ca²⁺ transient and triggered by the control AP (left) and post-MI AP (right). D, peak intracellular [Ca²⁺] (left) is elevated 2.2-fold upon stimulation with a post-MI AP relative to the control AP while fractional cell shortening (right) is increased 2.7-fold. *P < 0.05.