Adenosine is a commonly used pharmaceutical stressor at cardiac magnetic resonance examinations to assess suspected chronic coronary syndrome (CCS). However, several studies have reported that the current use of adenosine does not induce adequate hyperemic response in a substantial number of patients, leading to false diagnostics. The aim of this trial is to investigate the hyperemic effect of the standard dose of adenosine (140 microgram/kg/min) to the high dose of adenosine (210 microgram/kg/min) to improve the diagnostic methods using adenosine as a stressor and ultimately improve treatment decisions and patient prognosis in CCS.

Inclusion Criteria:

Patients:

1. The subject has given their written consent to participate in the trial.
2. Are referred to Department of Clinical Physiology, Skåne University Hospital, for suspected or known CCS or heart failure
3. Matches the inclusion criteria for sex and age (6 females and 6 males from each group in each age decade from 40 to >80 years old)
4. Matches the inclusion criteria for no known heart failure (group b) or known heart failure (group c)
5. No caffein intake <24h prior to the examination

Healthy volunteers:

1. The subject has given their written consent to participate in the trial.
2. Matches the inclusion criteria for sex and age (6 females and 6 males from each group in each age decade from 40 to >80 years old)
3. No caffein intake <24h prior to the examination

Exclusion Criteria:

Patients:

1. Acute referral (in-house patients)
2. Clinically unstable
3. Acute chest pain
4. Severe or decompensated heart failure
5. Non sinus rhythm (e.g. atrial fibrillation)
6. Asthma or severe chronic obstructive pulmonary disease
7. Known chronic renal failure (eGFR <45mL/min/1.73m2)
8. AV-block II or III
9. Left Bundle Branch Block
10. Systolic blood pressure <90 mmHg or >230 mmHg at rest
11. Increased intracranial pressure
12. Known allergy or adverse reaction to adenosine or mannitol
13. Known allergy or adverse reaction to gadolinium contrast agents
14. Treatment with medication containing dipyradimol or teofyllamin/teofyllin
15. Claustrophobia
16. Devices contraindicated to CMR imaging (pacemaker, implants, intracranial clips etc)
17. Pregnancy or breast feeding (screened by question only)
18. Inability to give informed consent due to mental state, language difficulties etc

Healthy volunteers:

1. Any of the exclusion criteria for patients
2. Blood pressure > 140/90 measured according to clinical routine
3. Known systemic disease
4. Known cardiac disease
5. Cardiovascular medication
6. Medication that might influence cardiovascular health
7. Smoking

The subject will be blinded to the order of adenosine doses.