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To achieve scalability, a few resource-rich heterogeneous nodes are scattered in a wireless sensor network consisting of a large number of energy-constrained sensor nodes. Heterogeneous nodes are equipped with powerful radio transceiver and their main task is to organize a backbone communication network and to relay data to the sink. For the scenario, this paper proposes a coverage problem which maintaining relay connectivity at the same time in heterogeneous wireless sensor networks. The goal is to find a minimum relay connected set cover (MRCSC) which satisfies (1) active nodes in set cover fully sense the whole task area. Motivated by triangular lattice with asymptotic optimality, we address a rule for restricting irregularity spread to form an approximate nice triangular lattice, (2) active nodes are relay connected which means any active node connects to at least one heterogeneous node with a given success data forwarding rate. Simulations show that the coverage of MRCSC nearly reaches that of OGCD, but relay connectivity of active nodes is strongly reinforced with limited count of additional nodes.