This applet is used to simulate the activation of human ventricular epicardial, endocardial, and midmyocardial cells using a 4-variable phenomenological model. The model reproduces various experimental data such as (dv/dt)_max, as well as human APD and CV restitutions (by A. Bueno, E. Cherry and F. Fenton, manuscript in preparation)

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, gate variables, 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 "Current and Ascii" to plot the total current of the model or obtain ascii data of Voltage vs t.

Things to try:

• Uncheck the Voltage box and check the boxes for some of the concentrations (last four checkboxes). Then change N to 300 or higher and see how the concentrations change over time.
• Change the cell type using the choice button.
• 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.)