Future wireless networks will coexist and combine resources over an IP-based infrastructure for ubiquitous connection support. Thus, to support non-perceptible connection migration between the heterogeneous wireless networks in this converged environment during mobility, seamless vertical handover mechanisms are a necessary requirement. Seamless handover mechanisms ensure non-perceptible interruptions to traffic flow of ongoing communications at a mobile device during the handover process. Various mobility management protocols have been proposed and standardized to support mobility across the heterogeneous wireless networks but they cannot provide seamless handover in their current form. We propose to optimize Proxy Mobile IPv6 with a special relay called the handover coordinator to further improve the handover performance in terms of handover delay and packet loss. Simulation results show that indeed PMIPv6 enhanced with the handover coordinator performs better than ordinary PMIPv6.