The many-to-one traffic pattern dominates in sensor networks, where a large number of sensor nodes send data to one sink. A sensor node may only communicate with a small portion of its neighbors. Most existing key management schemes for sensor networks are designed to establish shared keys for all pairs of neighbor sensors, no matter whether they communicate with each other or not, and this causes large overhead. To achieve better security and performance, we adopt a Heterogeneous Sensor Network (HSN) model. In this paper, we propose a novel routing-driven key management scheme, which only establishes shared keys for neighbor sensors that may communicate with each other. Recent work has demonstrated the feasibility of implementing Elliptic Curve Cryptography on small sensor nodes. We utilize Elliptic Curve Cryptography to design an efficient key management scheme for HSN. The performance evaluation and security analysis show that our key management scheme can provide better security with significant saving on sensor storage space and energy consumption than some existing key management schemes.