Inclusion Criteria:  18 - 80 years of age The patient is scheduled for open cardiac coronary arterial bypass graft (CABG) OR single heart valve surgery that require median sternotomy under general anesthesia Patients that are estimated to be weaned from mechanical ventilator not later than 8 h after surgery Patients that are capable of using the patient controlled analgesia device (PCA) after surgery Written informed consent from the patient  Exclusion Criteria:  A previous history of intolerance to the study drug or related compounds and additives Redo surgery Combined CABG and heart valve surgery Endocarditis and/or mediastinitis. Concomitant drug therapy with strong opioids or strong CYP3A4 or CYP2D6 inductor(s) or inhibitor(s) 2 weeks prior to study. Patients younger than 18 years or older than 80 years. Body weight < 60 kg BMI > 35, sleep apnoea, any other sleep disorder or condition that requires treatment with continuous positive airway pressure or automatic positive airway pressure device. Diagnosed hepatic cirrhosis or kidney disease: GFR < 29 ml/min/1,73 m2 or dependence on dialysis History of alcoholism, drug abuse, psychological or other emotional problems that are likely to invalidate informed consent. If the researcher judge, that the patient has a mental health disorder, retardation or other similar reason and do not have the capacity to give his/her consent to research or patient do not understand the meaning of the study, or is not able to use PCA device, the patient is to be exluded. History of alcoholism or drug abuse (especially opioid) may affect the use of opioid PCA device and make harm to the patient or invalid the study and are exluded. Cardiac insufficiency, ejection fraction (LVEF) < 30 % Patients with a diagnosis for neuropathic pain or chronic pain syndrome Insulin dependent diabetes mellitus with neuropathy Participation in any other study concomitantly or within one month prior to the entry into this study Donation of blood for 4 weeks prior and during the study Pregnancy or breastfeeding