Chronic mitral regurgitation is the most common valvular abnormality worldwide, it occurs in 10% of the general population and its prevalence increases with age. When left untreated, it can lead to left ventricular dysfunction and cause disabling symptoms (e.g., fatigue and dyspnea), life-threatening complications (e.g., ventricular dilation, congestive heart failure) and death. Surgical correction of chronic mitral regurgitation before irreversible changes happen can be curative. Open surgical valve repair or replacement are accomplished through cardiopulmonary bypass and cardioplegic arrest. Myocardial protection is essential to guarantee an uneventful perioperative course since a not-well protected heart may lead to postoperative low-cardiac output syndrome. This occurs in 30% of high-risk patients who undergo elective cardiac surgery and is associated with 20% mortality. Cardioplegia preserves the heart during ischemic arrest by reducing its metabolic demand. The most effective cardioplegia for protection in adult cardiac surgery remains unknown and improving the protection of the heart during the ischemic arrest may potentially improve patients' postoperative outcomes. Pharmacological adjuvants to the cardioplegic solutions have been tested to mitigate the ischaemic-reperfusion injury following cardiac surgery. Ultra-short acting beta-blockers (e.g., esmolol, landiolol) decrease intraoperative myocardial metabolic demand and suppress the sympathetic response to surgical stimuli while exhibiting limited adverse effects. Few studies with limited sample size investigated the role of ultra-short acting beta-blockers in reducing perioperative ischaemia and arrhythmia after cardiac surgery. When ultra-short acting beta-blockers were administered before aortic cross-clamping and as cardioplegia adjuvant we observed a trend towards a reduction in postoperative low-cardiac output syndrome (13/98 vs 6/102; p=0.08) and in the rate of hospital re-admission at one year (26/95 v 16/96, p=0.08) with an increase in the number of patients with ejection fraction \>60% at hospital discharge (4/95 vs 11/92, p=0.06) (Zangrillo 2021). However, despite a growing body of literature exploring the role of ultra-short acting beta-blockers in enhancing myocardial protection during on-pump cardiac surgery, further high-quality evidence is needed before this practice can be established as standard routine care. Hence, we designed a randomized, placebo-controlled trial involving 1500 patients undergoing open mitral valve surgery to assess the effect of administering landiolol as cardioplegia adjuvant to reduce the occurrence of postoperative low-cardiac output syndrome. Successful results would have a significant impact on short and long-term complications.