This model is used to simulate the activation of human atrial cells using the model of A Nygren, C. Fiset, L. Firek, J.W. Clark, D.S. Lindblad, R.B. Clark and W.R. Giles, 1998, Circulation Research, 82, 63-81. As in the other applets, one can change the time for the second stimulus (S2), calculate APD vs DI, and plot all the variables of the model.