Figure 8.

Chemo-electro-mechanical coupling in the human heart. Spatio-temporal evolution of the fiber contraction λ_ff, the transmembrane potential ϕ, the intracellular sodium, potassium, and calcium concentrations c_Na, c_K, and c_Ca, and the calcium concentration in the sarcoplasmic reticulum $c_{\text{Ca}}^{\text{sr}}$ during the gradual repolarization phase of the cardiac cycle. Changes in the individual ion concentrations initiate a slow decrease in the transmembrane potential ϕ from +20 mV to -86 mV. A decrease in the intracellular calcium concentration c_Ca initiates mechanical relaxation with λ_ff returning gradually to 0%. During the filling phase, the apex moves away from the base and the heart undergoes a counterclockwise rotation back to its original position.