A patient with an embolic stroke is receiving intravenous (I.V.) heparin sodium at 1400 units per hour via an intravenous infusion pump.  The healthcare provider orders warfarin sodium (Coumadin) 5mg orally to be administered daily for two days prior to discontinuing the intravenous heparin.   What is the rationale for continuing the I.V. heparin while the patient is being transitioned to oral anticoagulation with warfarin?  How would the nurse  promote patient safety while the patient is receiving these medications?