Abstract
The effect of training on the heart was studied morphologically with 61 Thoroughbred horses. On the basis of the training period, or the interval of time in months between the first and the last race trial, the horses were divided into four groups, A to D. Group A consisted of horses trained from 19 months on the average, group B of horses trained for 20 months on the average and then allowed to rest for 13 months on the average, group C of horses trained for 2 months on the average, and group D of untrained horses with no racing experience. The mean heart weight (and the rate of heart weight to body weight) was 4, 815+692 g (1.10+0.14 %) in group A, 4, 250±674 g (0.99±0.10 %) in group B, 4, 282±564 g (1.00±0.09 %) in group C, and 4, 134±550 g (0.94+0.16 %) in group D. There were significant difference in both weight and rate between groups A and D. The thickness of the left ventricular wall was 4.34, 4.07, 4.03, and 3.97 cm in groups A, B, C, and D, respectively. The thickness of the right ventricular wall was 2.25, 1.97, 2.13, and 2.04 cm in groups A, B, C, and D, respectively. There was little difference in the L/R ratio of ventricular mural thickness between groups A and D . In the Thoroughbred racehorse cardiac enlargement seemed to develop in both left and right ventricles at the same time .
