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The aim of the present study was to evaluate, if and to which extent echocardiographic B- and M-Mode measurements in horses are influenced by growth and training. 31 healthy Standardbred trotters from two different stables were divided into different groups, based on their age and training status and examined by echocardiography. A group of 10 yearlings (age group 1) was followed over the course of almost an year and examined at three different timepoints. At the time of the first examination the horses were unbroken and had no training history. At the time of the last examination the horses were fully trained and already competing in their first races (age group 2). This group was additionally compared to groups of three and four years old, fully trained Standardbreds (age groups 3 and 4), to evaluate, if a longer training period is essential to induce changes in the measured parameters. In the course of the 3 examinations within the first year of training heart size increased significantly. The inner diameter of the left ventricle increased by 8.5%, the left ventricular free wall by 27.5%, the aortic diameter by 7.1%, the left ventricular inner diameter by 15.1%, the pulmonary valve by 12.5%, the inner diameter of the left atrium measured from the left side by 13.98% at the level of the mitral valve and by 17.3% at the widest diameter. The right atrium also increased significantly over the 3 examinations by 9.39%. The left ventricular mass increased continuously from the first to the third measurement by 42.9% (P ≤ 0.0001). The mean wall thickness increased by 11.1% (P ≤ 0.003) from the first to the third examination. When comparing the measured parameters between fully-trained horses of age groups 2, 3 and 4 the pulmonary valve diameter was found to be significantly increased by 9.1% between age groups 2 and 3. The left ventricular inner diameter also increased measured above the papillary muscle (LVID, 4.5%, P = 0.027) as well as at the level of the papillary muscle (LV2, 7.3%, P = 0.04) in older horses. These differences of LVID and the pulmonary valve were also found between age groups 2 and 4. In addition, a significant increase of the thickness of the interventricular septum by 11.8% was found as well as a weakly significant increase of the thickness of the left ventricular free wall by 10% and the left ventricular wall by 11.2%. The diameters of the left atrium and the right ventricular inner diameter tended to increase between age groups 2, 3 and 4, but these differences were not statistically significant. Significant differences between age groups 3 and 4 were found for the left ventricular free wall (+ 17.4%, P=0.002) and the right atrium (+ 9.8%, P = 0.014). The left ventricular mass increased between age group 2 and horses of groups 3 and 4 by 12.7% (P=0.041). Standard echocardiographic examinations over the course of 3 timepoints in age group 1 and in comparison of age group 2 to horses of groups 3 and 4 showed a significant increase of left ventricular mass (LVM), left ventricular inner diameter and the thickness of the left ventricular free wall, while the relative wall thickness did not change. Therefore, a development of an eccentric cardiac hypertrophy, as commonly seen in endurance athletes and racehorses, was observed.