Echocardiographic values need to be established for each age and breed to be applied to equine medicine. The present research aims to describe echocardiographic measurements in Spanish fillies and colts of different age, to compare these values with those previously described for other equine breeds and to determine whether there is an influence of gender on echocardiographic measurements. Seventy unsedated and healthy Spanish foals of both sexes (39 females and 31 males) were divided into five age groups: A (22-60 days; n=15), B (61-90 days; n=13), C (91-180 days; n=18), D (181-270 days; n=12) and E (271-394 days; n=12). The following echocardiographic measurements were made: left ventricular internal dimensions, left ventricular free wall thickness and interventricular septum thickness at systole and at diastole. Mitral and tricuspid valve thickness was also determined. Opening velocity of the mitral valve in early diastole (DE slope), pattern of transmitral flow (E/A ratio) and echocardiographic mitral valve E point-septal separation (EPSS) were calculated from specific points in the anterior leaflet of the mitral valve. Aorta diameters were measured at the level of the valve leaflets, at the sino-tubular junction, at the valve level and at the sinus of Valsalva. Performance indices of the left ventricle were obtained. Most of the echocardiographic parameters increased with age, being the increases more marked up to 180 days of age. Fraction shortening, ejection fraction, stroke volume index, fractional septum and fractional wall thickening did not differ between groups. Some differences were found between fillies and colts in the different age groups, which could have been linked to the different body weight.