This paper studies a new symmetric two-user Gaussian interference channel (IC) in heterogeneous networks where two transmitter-receiver pairs are underlaid with one primary transmitter-receiver pair. When underlay transmitters must restrict their transmission to guarantee target degrees of freedom (DoF) of a primary receiver, the achievable DoF of the underlay receivers in heterogeneous networks is investigated. Either transmit power or transmission time is regulated to secure the target DoF of a primary receiver and their effects on the achievable DoF are analyzed for the simple Han-Kobayashi scheme. Our analytical results show that the achievable DoF of the underlay two-user IC is substantially different from that of a conventional two-user IC due to the imposed restriction on the underlay users. It is also shown that joint decoding capability at the primary receiver using common codebook relaxes the restriction imposed on the underlay users and hence improves the achievable DoF of the underlay receivers.