Transluminal balloon angioplasty is an option for treatment of post subarachnoid hemorrhage cerebral vasospasm. It is an invasive procedure that carries a risk of vessel perforation (by microguidewire) or rupture (by balloon inflation). However, when successful its effects persist, in contrast to the often transient effects of intra-arterial vasospasm treatment with calcium channel blockers such as Nimodipine or Verapamil ("chemical angioplasty"). For this reason it may be employed when there is difficulty in assessing the patient clinically, e.g. in high WFNS grade subarachnoid hemorrhage when the patient might be ventilated and sedated.