The final state interaction of pions in $K_{e4}$ decay allows one to obtain the value of the isospin and angular momentum zero $pipi$ scattering length $a_0^0$.We take into account the electromagnetic interaction of pions and isospin symmetry breakin
g effects caused by different masses of neutral and charged pions and estimate the impact of these effects on the procedure of scattering length extraction from $K_{e4}$ decay.
