Potassium permanganate decomposes when heated, the oxidation state of manganese changes as the oxidation state of ${\mathrm{KMnO}}_4$ is $+7$ decomposes to potassium manganate which oxidation state is $+6$ and manganese dioxide its oxidation state is $+4$.

It is a redox reaction in which $\mathrm{Mn}$ which undergo both oxidation and reduction such type of reaction is known as a disproportionation reaction.

$2{\mathrm{KMnO}}_4\stackrel{513 \mathrm{K}}{\to }{\mathrm{K}}_2{\mathrm{MnO}}_4+{\mathrm{MnO}}_2+{\mathrm{O}}_2$