Cardiovascular disease and ischemic heart disease is the #1 killer in Canada. Currently, Cardiac invasive catheterization angiography (CICA) is the gold standard for the assessment of the arteries in the heart. However, cardiac catheterization has risks which prohibit its use in all patients. These risks include: death, heart attack, stroke and bleeding. Cardiac computed tomography angiography (CTA) is a new non-invasive technology which may enable the evaluation of patients' coronary anatomy without exposing patients to the risks of invasive cardiac catheterization.

The purpose of this project is to compare CT angiography (CTA) to Tc-99m single photon emission computed tomography (Tc-99m SPECT)

We will enroll patients who are waiting for a CICA or who have been referred for a TC-99m SPECT or CTA scans at the University of Ottawa Heart Institute. Consenting patients who are waiting for a CICA will have both a CTA and a Tc-99m SPECT scan. Consenting patients referred for a CTA or Tc-99m SPECT will have both the CTA and Tc-99m SPECT in a random order but not CICA (unless ordered by your physician).

Inclusion Criteria:

• Patients referred for Tc-99m SPECT or CTA; or
• Patients referred for CICA without preceding (< 12 months) MPI or CTA

Exclusion Criteria:

• Previous revascularization (PCI or CABG)
• Age < 18 years or lack of consent
• Renal Insufficiency (GFR < 60 ml/min)
• Allergy or contraindication to contrast agent or dipyridamole
• Refractory angina requiring urgent/emergent coronary angiography
• Contraindication to radiation exposure (e.g. pregnancy)
• Uncontrolled HR
• Atrial fibrillation, frequent atrial or ventricular ectopy (> 1/minute)
• Unable to perform 10 second breath-hold