Heart size and heart rate variability of the top earning racehorse in Japan, T. M. Opera O

Abstract

T. M. Opera O is considered as one of the greatest racehorses in the history of horseracing in Japan. Only a very few data is available on circulatory function of elite Thoroughbred racehorses. Recently, we obtained data on circulatory parameters of T. M. Opera O. The left ventricular mass of T. M. Opera O, as measured on an echocardiogram, was 4.60 kg. The resting heart rate (HR) of T. M. Opera O was 25 beat/min. The low-frequency and high-frequency power, as determined by an analysis of HR variability, were 13,900 and 5.963 ms2, respectively, which were considerably higher than those of the other racehorses. These results suggest that a large heart, formed by genetic factors and training, markedly enhanced the parasympathetic nervous activity and reduced the resting HR of T. M. Opera O. The data we obtained from T. M. Opera O is invaluable for understanding the physical fitness of elite Thoroughbreds and for further developing their athletic performance.