A clinical trial to be conducted in many hospitals and in different countries with the medicinal substance Regadenoson to be used in a type of heart scan called 'radionuclide myocardial perfusion imaging' to see the blood flow in the heart muscle in patients aged between 1 month - 18 years.

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• Patients must be excluded from participating in this study if they meet any of the following criteria: 1. Prior allergic reaction to Gd contrast agents and/or regadenoson or any component of its formulation or to aminophylline or to its components (ethylenediamine and theophylline). 2. Standard clinical contraindications to MRI as per institutional guidance, including patients with cochlear implants and implanted cardiac devices, or considered unfit for a pharmacologic stress perfusion CMR test by the investigator. 3. All patients will be screened for eGFR within 24 hours before the exam, and patients presenting with eGFR <30 mL/min/1.73 m2 (by the Schwartz formula) will be excluded. 4. Pregnant or lactating females or females of childbearing potential not using an acceptable form of birth control (negative urine pregnancy test also required). 5. In the judgment of the investigator, any clinically significant ongoing medical condition (e.g., myocardial infarction, or unstable angina within 5 days, pericardial inflammatory disease, severe cardiac outflow tract obstruction, acutely decompensated heart failure, uncontrolled epilepsy, high risk for seizures, etc.) or clinically significant laboratory abnormality that is considered to potentially jeopardise the patient’s safety. 6. Patients with 2nd or 3rd degree atrioventricular block or sick sinus syndrome with or without an artificial pacemaker. 7. Known or suspected bronchoconstrictive and bronchospastic lung disease either being unstable or requiring active treatment (e.g., wheezing noted on physical exam, frequent exacerbations, or active treatment with a bronchodilator or corticosteroids). 8. Out of acceptable range sitting or semi-recumbent resting BP or HR (beats per minute [bpm]) at screening and dosing day as provided below: a) Acceptable range for BP (systolic / diastolic mmHg): 85 to 130 / 45 to 90 b) Acceptable range for HR: 55 to 100 bpm for 12 to <18 years old, and 60 to 120 bpm for 2 to <12 years old. 9. Use of any experimental or investigational drug or device within 30 days prior to dosing with study drug. 10. Consumption of methylxanthine-containing products such as caffeinated coffee, tea, caffeinated soft drinks, cocoa, or chocolate in the 48 hours prior to dosing. 11. Aminophylline or theophylline use within 24 hours, dipyridamole use within 48 hours prior to dosing. 12. History of alcohol abuse or drug addiction. 13. Positive urine drug screen at the screening visit, including amphetamines, barbiturates, cannabinoids, cocaine, ethanol and opiates, unless it is a prescribed medication containing any of these ingredients, the investigator finds it acceptable, and after agreement from the Sponsor medical monitor. 14. Currently smokes more than 5 cigarettes or equivalent per day, and if eligible for the study, would not be able to abstain from smoking from midnight prior to dosing until the end of the study period.