Calcium is essential for the normal functioning of the heart. During the cardiac action potential (i.e. excitation of the heart), calcium enters cardiac muscle cells from the extracellular fluid, and is also released from internal stores in the sarcoplasmic reticulum (i.e. calcium-induced calcium release). In this simulation you will test the effect of changing the extracellular calcium concentrations on the force of contraction (tension) produced.

1. Press the Start button and observe your recording.
2. Using the dropdown box select Calcium free solution and click the Change calcium button and observe your recording. What happens to the force of contraction? Why does this happen?
3. Next using the dropdown box, select:
   (1) 0.2 mM calcium
   (2) 0.8 mM calcium solution and finally
   (3) 2.0 mM calcium solution in order to increase the extracellular calcium concentration. What happens to the force of contraction? Why does this happen?

View the video below before commencing this simulation.