Diastolic dysfunction of the heart is correlated with cardiac mortality. Serum 
cystatin C (CysC) is an endogenous marker of kidney function. It is not clear 
whether serum CysC is associated with diastolic dysfunction in patients with 
varying cardiac conditions with concomitant diastolic abnormalities and 
preserved ejection fraction (EF). The authors measured serum CysC levels in 
patients with cardiac diseases and examined the relationships between serum CysC 
levels and diastolic function. Serum CysC was measured and echocardiography was 
performed in 124 consecutive patients with cardiac diseases. Transmitral flow 
(TMF) patterns surrogating diastolic function were categorized into two groups: 
a normal group and an abnormal group. Serum CysC and BNP showed a significant 
positive correlation. There were no significant differences in serum CysC among 
those cardiac diseases. Seventy-eight patients with cardiac disease and 
preserved EF (left ventricular EF ≥50%) and without renal dysfunction (estimated 
glomerular filtration rate ≥60 mL/minute/1.73 m(2) ) were examined. Multivariate 
linear regression analysis demonstrated that left atrium diameter and abnormal 
TMF patterns were independent determinants of serum CysC. Furthermore, patients 
with elevated serum CysC levels had poor prognosis. Serum CysC is associated 
with diastolic dysfunction in patients with various cardiac diseases and 
preserved EF. Serum CysC might be a biomarker of cardiac diastolic dysfunction 
in patients with preserved EF.