 Although adenosine stress CMR is a rapidly maturing test, several important challenges exist. First, many patients find it difficult to tolerate the common side effects of adenosine in the confined space of the MRI scanner. Secondly, many patients under the influence of adenosine and its side effects cannot adequately hold their breath during image acquisition making image interpretation more difficult and quantitative analysis very time consuming. Finally, because adenosine must be continuously infused during a contrast-enhanced stress CMR, 2 separate intravenous I.V. catheters are needed. Most of the undesirable effects of adenosine are mediated through the adenosine A2B and A3 receptors; where as, its desired vasodilator effects are mediated through the A2A receptor. The FDA recently approved an adenosine A2A receptor specific stress testing agent called regadenoson which is administered as a 10 second bolus and has an improved side effect and safety profile when compared to adenosine. With its improved tolerability and ease of use, regadenoson is a more ideal stress testing agent to use with CMR. 