Following is a summary of two variable models of excitable media. Two variable models that we describe here are always of the form

$$C_m{dv\over dt} = F(v,w)$$ (1)

$${dw\over dt} = G(v,w)$$ (2)

Typically, $v$ is a ``fast'' variable, while $w$ is a ``slow'' variable. The remaining sections are to specify the functions $F(v,w)$ and $G(v,w)$.