Background: Heart failure with preserved ejection fraction (HFpEF) is frequently observed in older women. Increased arterial stiffness in this population may be a cause of HFpEF. Methods and Results: In 75 patients who underwent cardiac catheterization and who had no significant coronary artery stenosis or left ventricular (LV) wall motion abnormalities, the LV relaxation time constant (Tp) was calculated. The LVEF was obtained from left ventriculography, and plasma brain natriuretic peptide (BNP) level was measured. From the pressure waveforms at the ascending aorta, the augmentation index (AIx) was calculated. Effective arterial elastance (Ea) and total vascular resistance (TVR) were also determined. No significant differences were found between genders for age, heart rate, central blood pressure, or LVEF. Ea, TVR, AIx, and BNP level were significantly greater in women than in men, but only AIx was significantly correlated with Tp (r=0.25, P=0.04) and BNP level (r=0.33, P=0.005). Conclusions: The arterial system is stiffer in women than in men of the same age. Among the parameters of arterial stiffness, only AIx is related to abnormal LV relaxation and increased BNP level. Elevated AIx is a factor that causes LV diastolic dysfunction and may be associated with the development of HFpEF in this gender.  (Circ J 2013; 77: 123–129)