Many stress tests being done today have two parts, the stress test and the pictures of your heart. The investigators are comparing a newer technique to obtain the pictures (PET imaging) to the standard method (SPECT imaging). However, it is not known if the new test is better than the old test. It is important to have a standard to compare these tests to, and that is why people who will be getting a cardiac catheterization are being asked to participate. The information about your arteries from the cardiac catheterization will be used to judge which stress test is better. The investigators hypothesize that the newer method (PET imaging) will be more accurate than the old method (SPECT) in detecting heart disease.

A SPECT rest image will be obtained using a technetium based isotope. On a separate day, a Rubidium rest PET image will be obtained prior to a Dipyridamole stress test. Subjects will receive both Rubidium and technetium isotopes following the Dipyridamole stress, and will undergo first PET imaging and later SPECT imaging following the stress test. Patients will then go for cardiac catheterization as clinically ordered by their physician.

Inclusion Criteria:

• referred for clinical cardiac catheterization

Exclusion Criteria:

• previous CABG
• previous MI
• Asthma or obstructive airway disease
• Intolerance to Dipyridamole
• Moderate to severe valvular disease
• Cardiomyopathy - (ejection fraction less than 45%)

Patients with intermediate to high likelihood of CAD referred for cardiac catheterization, either on outpatient or inpatient basis