This paper is concerned with the chaos of discrete dynamical systems. A new concept of heteroclinic cycles connecting expanding periodic points is raised, and by a novel method, we prove an invariant subsystem is topologically conjugate to the one-side symbolic system. Thus, heteroclinic cycles imply chaos in the sense of Devaney. In addition, if a continuous differential map
h
has heteroclinic cycles in
ℝ
n
, then
g
has heteroclinic cycles with
h
−
g
C
1
being sufficiently small. The results demonstrate
C
1
structural stability of heteroclinic cycles. In the end, two examples are given to illustrate our theoretical results and applications.