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Objective--To characterize systolic intervals of the left ventricle and their relationship with heart rate in conscious sheep. Animals--11 healthy Romanov sheep (age range, 3 months to 10 years). Procedures--Systolic intervals and indices of myocardial contractility of the left ventricle were measured in conscious sheep by use of polycardiography. Results--The mean ± SD pre-ejection period was 59 ± 12 milliseconds, and the mean left ventricular ejection time was 194 ± 34 milliseconds. The mean myocardial tension index was 0.22 ± 0.05, and the mean ratio of the pre-ejection period to ejection time was 0.30 ± 0.09. Total electromechanical systole, mechanical systole, and ejection time varied inversely with heart rate. The electromechanical delay and pre-ejection period were not correlated with heart rate, nor were the myocardial tension index and the ratio of the pre-ejection period to ejection time. The isovolumetric contraction index and isovolumetric contraction time were not significantly correlated with heart rate, although the values for the correlation coefficient,were moderate (r =-0.561 and r =-0.482, respectively). Conclusions and Clinical Relevance--Although a larger study would be needed to provide reference intervals for healthy sheep, the results of the study reported here provided useful information for the cardiac evaluation of sheep. (Am J Vet Res 2009;70:330-333) [ABSTRACT FROM AUTHOR]