Background: Non-steroidal anti-inflammatory drugs (NSAIDs) are recommended for the management of acute postoperative pain as part of a multimodal strategy to reduce opioid use, relieve pain, and reduce chronic pain in non-cardiac surgery. However, significant concerns arise in cardiac surgery due to the potential adverse effects of NSAID including increased bleeding and acute kidney injury (AKI). We hypothesized that NSAIDs are effective against pain and safe in the early postoperative period following cardiac surgery, taking contraindications into account. Methods: The KETOPAIN trial is a prospective, double blind, 1:1 ratio, versus placebo multicentric trial, randomizing 238 patients scheduled for cardiac surgery. Written consent will be obtained for all participants. The inclusion criterion is patients more than 18 years old undergoing for elective cardiac surgery under cardiopulmonary bypass (CPB). Patients will be allocated to the intervention (ketoprofen) group (n = 119) or the control (placebo) group (n = 119). In the intervention group, in addition to the standard treatment, patients will receive NSAIDs (ketoprofen) at a dose of 100 mg each 12 h 48 h after. The control group, in addition to the standard treatment, will receive a placebo of NSAIDs every 12 h for 48 h after surgery. An intention-to-treat analysis will be performed. The primary endpoint will be the intensity of acute postoperative pain at rest at 24 h from the end of surgery. Pain will be assessed using the numerous rating scale. The secondary endpoints will be postoperative pain on coughing during chest physiotherapy, postoperative pain until day 7, the pain trajectory between day 3 and day 7, cumulative opioid consumption within 48 h after surgery, nausea and vomiting, the occurrence of postoperative pulmonary complications within the first 7 days after surgery, neuropathic pain at 3 months, and quality of life at 3 months. Discussion: NSAIDs function as non-selective, reversible inhibitors of the cyclooxygenase enzyme and play a role in a multimodal pain management approach. While there are recommendations supporting the use of NSAIDs in major non-cardiac surgery, recent guidelines do not favor their use in cardiac surgery. However, this is based on low-quality evidence. Major concerns regarding NSAID use in cardiac surgery patients are potential increase in postoperative bleeding or AKI. However, few studies support the possible use of NSAIDs without the risk of bleeding and/or AKI. Also, in a recent French survey, many anesthesiologists reported using NSAIDs in cardiac surgery. To date, no large randomized study has been conducted to evaluate the efficacy of NSAIDs in the management of postoperative pain in cardiac surgery. The expected outcome of this study is an improvement in the management of acute postoperative pain in cardiac surgery with a multimodal strategy including the use of NSAIDs.