Wireless sensor networks (WSNs) composed of a large number of nominal power nodes, having limited processing, communication, and storage resources. Large scale WSNs are highly susceptible to different network attacks. These attacks can be mitigated by providing the standard security requirements of confidentiality, authentication and availability in WSNs. These security requirements can be achieved by encryption and authentication services, which demand a comprehensive key management scheme. Key management in WSNs is difficult due to the unknown network topology prior to deployment, sporadic connectivity and scarce resources of the sensor network environment. This work presents key management scheme for hierarchical Heterogeneous Sensor Networks (HSN) consisting of a small number of high-end sensors and a large number of low-end sensors. A key generation process is incorporated, where a small number of generation keys are used to generate a large pool of random symmetric keys, in order to address storage overhead problem in the constraint sensor nodes. In addition, a self-healing group key distribution scheme is developed for secure multicast communications in HSN environment.