Transient cortical blindness is a known complication after cerebral and vertebral angiography although is a rare complication following cardiac catheterization. In this report, we describe a seventy-six-year-old male patient who had cortical blindness after coronary bypass graft angiography. The development of cortical blindness, in this setting, appears to be an osmotic disruption of the blood-brain barrier which is selective for the occipital cortex. Other hypotheses, such as an immunological reaction to the contrast agent or a direct injection of dye into the vertebral artery system, were considered. The clinical outcome is usually favourable, with vision completely restored within 24-48 hours, as was the case of the patient described in the present report.