One of the simplest single cell models is what is now called the FitzHugh–Nagumo (FHN) model. The model was originally developed as simplification of the Hodgkin–Huxley model by FitzHugh. It exists many variations of the original FHN model. The aim of this paper is to find the parameter thresholds used in FHN model for regular excitation. The thresholds of different parameters are presented. We observe that regular activation occurred when the excitation current is above a threshold level. Sensitivity of different FitzHugh-Nagumo parameters on cardiac excitation is observed. This study represents the first stage toward the development of an accurate computer model of heart activation.