  We report a three-variable simplified model of excitation fronts in human
atrial tissue. The model is derived by novel asymptotic techniques \new{from
the biophysically realistic model of Courtemanche et al (1998) in extension of
our previous similar models. An iterative analytical solution of the model is
presented which is in excellent quantitative agreement with the realistic
model. It opens new possibilities for analytical studies as well as for
efficient numerical simulation of this and other cardiac models of similar
structure.
