Acute kidney injury (AKI) is a common complication after cardiac surgery. Mismatch in renal oxygen demand-supply may be an important pathogenetic factor. Levosimendan has been shown to improve renal blood flow, glomerular filtration rate and renal oxygenation in healthy controls after cardiac surgery.

In order to investigate the effect of levosimendan in patients with AKI after cardiac surgery, the investigators plan a randomized placebo controlled trial. 30 patients will receive levosimendan or placebo. Renal blood flow and filtration fraction will be measured using infusion clearance technique of para-aminohippuric acid and Chromium ethylenediaminetetraacetic acid (Cr-EDTA) respectively.

Inclusion Criteria:

• Patients in the cardiothoracic intensive care after cardiac surgery with cardiopulmonary bypass
• Acute kidney injury, defined as increase in S-creatinine 50% or 27 mol/L
• Normal S-creatinine before surgery

Exclusion Criteria:

• Ongoing treatment with inotropic drugs (not norepinephrine)
• Central venous oxygen saturation (ScvO2) < 60% despite optimization of hematocrit and volume status
• Need of renal replacement therapy
• Ongoing bleeding
• Patient or next of kin does not consent with study participation