The article synchronization is one of the most fundamental issues in online social networking services. In particular, an efficient synchronization scheme should be devised when users enjoy online social networking services in heterogeneous wireless networks where multiple access networks with different transmission costs are deployed. In this paper, we propose an opportunistic push scheme (OPS) that aggregates the published articles and pushes opportunistically the aggregated articles through low-cost access networks (e.g., open WiFi networks). To balance the reduced transmission cost and the consistency of articles, a Markov decision process (MDP) problem is formulated and the optimal policy is determined. Numerical results demonstrate that OPS with the optimal policy can reduce the number of transmissions in high-cost access networks while satisfying users' quality of experience (QoE) in terms of the article consistency.