This applet is used to simulate the activation of human left ventricular epicardial myocytes using the 67-variable model of V. Iyer, R. Mazhari, and R.L. Winslow (Biophys J 2004; 87: 1507-1525).

Using the applet, the myocyte can be paced at various cycle lengths and the final APD and DI are calculated automatically. In addition, it is possible to visualize the currents, channel open probabilities, gate variable, and ionic concentrations.

N(S1's) indicates how many S1 stimuli to apply.
• S1 (bcl) indicates the cycle length for the S1 stimuli.
• S2 (bcl) indicates the cycle length for the S2 stimulus.

Click "Start" to start the simulation. Use "Replot" to replot on the screen once a check box has been selected or a new value has been entered for S1, S2 or N. Use "Plot Currents" to plot the various currents of the model.

Things to try:

• Uncheck the Voltage box and check the boxes for some of the concentrations (last four checkboxes). Then change N to 100 or higher and see how the concentrations change over time.
• To calculate points on APD restitution curves, change N, S1, and S2.
• Click in the Ascii check box to obtain the voltage signal as a function of time. (Note that the larger the signal, the longer it takes for the window to appear.)