This study will involve patients who are planned to have hip or knee replacement surgeries. They will undergo a Transthoracic Echocardiogram study (an ultrasound of the heart) to look for a Patent Foramen Ovale (PFO). A PFO is a hole in the heart that everyone is born with and in most cases eventually closes by adulthood. However, it does not always close in all people. The investigators will compare the participants as two groups - those with a PFO, and those without, and look for differences in delirium in their postoperative stay. This will help us look for an association between postoperative delirium and the presence of a PFO.

Inclusion Criteria:

• Planned to undergo an elective, primary hip replacement surgery or knee replacement surgery
• Fluent in English

Exclusion Criteria:

• Planned to undergo a revision knee or hip replacement
• History of cardiac surgery or prosthetic heart valves
• History of other structural heart abnormalities, not involving the atrial septum
• History of preexisting neurologic condition that affects the patient's day-to-day life, including a history of Dementia, Stroke, or previous Neurosurgery causing ongoing problems
• Significant visual problems felt by investigators to impair Confusion Assessment Method use
• Significant hearing problems felt by investigators to impair Confusion Assessment Method use
• History of psychiatric problems requiring treatment with major antidepressant drugs or antipsychotic drugs
• History of a Deep Venous Thrombosis or Pulmonary Embolism in the past year
• History of known Atrial Fibrillation in the past 3 months
• Presence of a pacemaker or implantable cardioverter-defibrillator
• History of Transient Ischemic Attack or Stroke within the past year

The study population will involve adult patients planned to undergo an elective, primary hip or knee replacement surgery at one of the hospitals of the London Health Sciences Centre (University Hospital or Victoria Hospital).