The investigators goal is to determine whether cardiopulmonary exercise testing (CPET) can be utilized in the diagnosis of myocardial ischemia. For the study participants the investigators will recruit patients who have been referred to myocardial perfusion PET/CT scan in Kuopio University Hospital. The participants will perform the CPET on a cycle ergometer on separate day after the perfusion scan. The investigators will compare the results of the PET/CT scan and CPET and evaluate if the possible perfusion defects detected in PET/CT correlate with the gas exchange parameters in CPET. The patients who receive invasive coronary treatment (coronary bypass surgery or percutaneous coronary intervention) will be invited to perform additional CPET ja PET/CT tests six months after the treatment. The goal will be to determine whether the recovery of myocardial perfusion can be assessed with gas exchange parameters in CPET.