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To evaluate a possible effect of cardiac deconditioning, a group of 2-year old healthy trotters was examined clinically and by echocardiography in racing condition and after a period of rest. Echocardiographic examinations included 2DE, M-mode, Doppler, TVI assessment (spectral and colour TVI) as well as speckle tracking analysis. Overall, 12 horses were examined twice (trained vs. rested) at a three month interval. Heart sized and myocardial thickness were evaluated by using 2DE and M-mode, all valves by colour Doppler. Myocardial velocities were measured by spectral and colour TVI in the left free ventricular wall, the interventricular septum and the right ventricular wall in radial orientation from right parasternal short-axis echocardiograms. Myocardial deformation parameters strain and strain rate were evaluated by speckle tracking analysis of the left ventricular wall and the interventricular septum from 2DE images. After three month of rest, a significant increase of the left ventricular free wall by 14.54% (P=0.006) was found in 2DE images compared to horses in race training. The left ventricular inner diameter had decreased by 4.99% (P=0.048). In addition, the isovolumetric relaxation time of the left ventricular free wall showed a significant reduction of 9.52% (P=0.040) in spectral Doppler imaging. Ejection time from the left ventricle was increased significantly by 4.69% (P=0.019) in colour TVI. Speckle tracking analysis showed a significant increase of early diastolic strain rate in the interventricular septum (P=0.020). There were no significant differences in all other parameters studied. As all horses had access to pasture during the resting period, voluntary exercise might have been sufficient to compensate for race training.