This study is for people who have a SPECT scan (nuclear imaging of the blood flow to the heart muscle) ordered by their medical doctors. As part of the SPECT scan, they will have been given a drug called regadenoson to widen and expand the blood vessels bringing blood to the heart muscle. The SPECT pictures of the heart are taken about an hour after the regadenoson is put into an arm vein through an IV. In this study, additional echo pictures will be taken and compared to the SPECT pictures.

The aim of the study is to see if the echo pictures work as well as SPECT to measure the blood flow to the heart muscle.

This is a single center, prospective, non-randomized, comparative, same-setting study of Lexiscan MPI SPECT versus state-of-the-art echocardiography. Lexiscan SPECT MPI will be performed per routine clinical protocol with Lexiscan administered as per package insert (0.4 mg in 5 ml IV push over 10 seconds followed by a 5 ml saline flush). Simultaneous echo/Doppler will be obtained immediately before (baseline), during and immediately post (peak vasodilation) using conventional techniques.

Inclusion Criteria:

• Patients referred to a University of Arizona/Sarver Heart Center/University Medical Center stress imaging laboratory and scheduled to receive a regadenoson SPECT nuclear scan.

Exclusion Criteria:

• Patients unable or unwilling to undergo the clinically necessary stress test or to provide informed consent.

Patients referred to a University of Arizona / Sarver Heart Center / University Medical Center stress imaging laboratory and scheduled to receive a regadenoson SPECT nuclear scan.