A new type of unstability of action potential propogating in spatially
inhomogenious electrically excitable media is announced. Numerical ex
periments with the FitzHugh-Nagumo model show that if the medium conta
ins a region where membrane slow, outward currents are partially depre
ssed then the back front of action potential passing through such a re
gion can split forming a <<burning drop>> - solitary standing wave of
depolarisation with finite <<life duration>>.