Myocardial contractility is best correlated with the intracellular concentration of

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[IV B 6]. Contractility of myocardial cells depends on the intracellular $\left[\mathrm{Ca}^{2+}\right]$, which is regulated by $\mathrm{Ca}^{2+}$ entry across the cell membrane during the plateau of the action potential and by $\mathrm{Ca}^{2+}$ uptake into and release from the sarcoplasmic reticulum (SR). $\mathrm{Ca}^{2+}$ binds to troponin $\mathrm{C}$ and removes the inhibition of actin-myosin interaction, allowing contraction (shortening) to occur.

Myocardial Contractility Is Best Correlated with the Intracellular Concentration of Na+\mathrm{Na}^{+}Na+

Myocardial Contractility Is Best Correlated with the Intracellular Concentration of $\mathrm{Na}^{+}$