A retrospective chart review was performed for identification of patients with isolated internuclear ophthalmoplegia (INO) postcardiac catheterization from two neuro-ophthalmology units. Of the 110 patients with a diagnosis of INO who were evaluated during the observation period, five patients (4.5%) demonstrated relatively isolated INO occurring in the perioperative period of a cardiac endovascular procedure. These five patients underwent diagnostic catheterization alone (three patients), balloon angioplasty (one patient), or stent placement (one patient). All patients improved, with resolution of diplopia in primary position after a mean period of 82 days. The occurrence of INO in the postcardiac catheterization setting is not uncommon, and it appears to be related to dorsal pontine ischemia. The pontomesencephalic medial longitudinal fasciculus is supplied by small-caliber perforating end-arteries from the basilar trunk, which increases selective vulnerability of this area. Cardiac catheterization may precipitate microemboli involving these vessels, leading to internuclear ophthalmoplegia.