OBJECTIVES: The slope in the preload recruitable stroke work relationship is a highly linear, load-insensitive contractile parameter. However, the perioperative change of the slope has not been reported before. We examined the perioperative slope from a steady-state single beat in patients with functional mitral regurgitation and assessed the correlation with brain natriuretic peptide (BNP) levels. METHODS: The study included 16 patients with non-ischemic dilated cardiomyopathy and refractory heart failure: 10 patients underwent mitral valve plasty and left ventricular plasty (MVP + LVP group) and 6 patients who underwent mitral valve replacement and papillary muscle tugging approximation (MVR + PMTA group). The left ventricular ejection fraction was assessed by the modified Simpson method; the slope was assessed by the single-beat technique using transthoracic echocardiography. BNP levels were measured by chemiluminescent immunoassay. RESULTS: The left ventricular ejection fraction and slope did not significantly change from pre- to early post-surgery in the MVP + LVP group. Both the left ventricular ejection fraction and slope significantly increased 6 months after surgery in the MVR + PMTA group. Postoperative BNP level was low in the MVR + PMTA group. While the postoperative left ventricular ejection fraction did not correlate with BNP levels, the postoperative slope significantly correlated with BNP level after surgery in the MVP + LVP group and in the total functional mitral regurgitation group. CONCLUSIONS: The change of slope was dependent on surgical procedures. In functional mitral regurgitation, the slope may be a more sensitive parameter in reflecting the left ventricular contractile function than the left ventricular ejection fraction.