A heterogeneous wireless IoT system is assumed to be used where several wireless subsystems with different standards using the same frequency coexist in a narrow space such as a factory. In the heterogeneous wireless IoT system, interference from the micro-cell system (μSystem) to the pico-cell system (pSystem) decreases the pSystem throughput. In this paper, we propose a Dual Clear to Send (Dual-CTS) method as a novel access control method for avoiding interference by exploiting spatial resources. In the proposed Dual-CTS method, μSystem gateway (μGW) does not broadcast only conventional CTS but also special CTS for pNode (pCTS) after receiving Require to Send (RTS). The pCTS enables pNode to transmit data using the same time and the same frequency resources as μNode uses. Calculation and simulation results show that the pSystem throughput in the proposed method is higher than one of the conventional methods by 1.3 times or more by exploiting the spatial resource.