Although pulse wave velocity is the primary indicator of arteriosclerosis and is widely used as an index of vascular age in anti-aging medicine, no index is available to quantify cardiac age. We proposed a "cardiac age" index and sought to clarify its clinical significance. The study subjects were 234 patients with atherosclerosis-related diseases. These patients were divided into 127 normotensive (mean age: 64+/-12 years) and 107 hypertensive (mean age: 65+/-11 years) patients. Echocardiography was performed, and brachial-ankle pulse wave velocity (baPWV) was measured using an automatic waveform analyzer. The index of cardiac age was determined as 1,000xVS(ot)/BSA/(VS-AO), where VSot (mm) was the ventricular septal thickness at the left ventricular outflow tract, BSA (m2) was the body surface area, and VS-AO (degree) was the angle between the basal ventricular septum and the ascending aorta. The index of cardiac aging correlated significantly with age in both the normotensive (r=0.63, p<0.001) and hypertensive (r=0.58, p<0.001) patients, and these correlations were closer than those between transmitral E/A (early to atrial velocity) ratio and age in normotensive (r=0.54, p<0.001) and hypertensive (r=0.44, p<0.001) patients. The slope between age (x-axis) and the index of cardiac age (y-axis) was greater in hypertensive (1.50) than normotensive (1.32) patients. Stepwise regression analysis showed that age (beta coefficient=0.35, p<0.001), the presence of hypertension (beta coefficient=0.26, p<0.001), the left ventricular mass index (beta coefficient=0.34, p<0.001), the left ventricular end-diastolic dimension (beta coefficient=-0.35, p<0.001), the dimension of the left atrium (beta coefficient=0.14, p=0.014), and the ratio of E to A (E/A) (beta coefficient=-0.12, p=0.046) were independently associated with the index of cardiac age. The index was also significantly correlated with baPWV (r=0.53, p<0.001). The proposed index of cardiac age can quantitatively assess cardiac morphological changes due to aging and/or hypertension and may be a useful marker of peripheral arterial stiffening.