There are only limited data about the role of renal function in the development of left ventricular systolic dysfunction in patients with an acute coronary syndrome (ACS). We sought to investigate whether renal insufficiency is an independent predictor for systolic dysfunction among patients who had an ACS.During 2006-2007, 814 consecutive patients who presented with an ACS event were enrolled prospectively; of these, 284 men (65 ± 14 years) and 71 women (71 ± 12 years) developed left ventricular systolic dysfunction (ejection fraction <40%), 306 men (64 ± 12 years) and 78 women (67 ± 10 years) had preserved left ventricular systolic function (ejection fraction >50%), while the rest of the patients (n=75), with ejection fraction between 40-50%, were excluded from this analysis. Creatinine clearance rates were estimated by the Cockcroft-Gault formula.Eight percent of patients presented with severe and 30% with moderate renal dysfunction. Multiple logistic regression analysis revealed that a 10-unit increase of creatinine clearance levels decreases the odds of developing left ventricular systolic dysfunction by 8% (95%CI per 1 unit: 0.986-0.998), after controlling for potential confounders. Moreover, brain natriuretic peptide levels were inversely correlated with creatinine clearance (r=-0.378, p<0.001). When brain natriuretic peptide was entered into the model, creatinine clearance was not associated with left ventricular systolic dysfunction (OR=0.997, 95%CI 0.989-1.005).The role of renal insufficiency in the development of left ventricular systolic dysfunction seems to be partially explained by plasma brain natriuretic peptide levels, suggesting a potential pathophysiological mechanism. Thus, patients with impaired creatinine levels and elevated brain natriuretic peptide levels should receive more aggressive medical care, as they are prone to developing left ventricular systolic dysfunction.