Maximal aerobic capacity, chest X ray, vectorcardiographic, and echocardiographic examination were undertaken once a year for two years during the course of training in 12 young male long distance runners starting from 18~19 years, who belonged to college or company track team.
　Cardiac volume and left ventricular mass were significantly increased for two years. Significant increases in the interventricular septum and left ventricular posterior wall was also observed but no difference was made in the left ventricular internal diameter, stroke volume, and ejection fraction. These findings suggest that cardiac enlargement observed in the present study resulted from thickening of the IST and PWT.
　Maximal aerobic capacity and athletic performance remained unchanged. There were no relationship between the change in LV mass and VO₂max. It seems probable that cardiac enlargement observed in athletes does not necessarily occur in parallel with increase of aerobic capacity.
　Significant increase was observed in maximal QRS vector amplitude, which shows the left ventricular hypertrophy. Otherwise, maximal QRS vector tended to be directed anteriorly. It is suggested that the right ventricular hypertrophy occurred following endurance training.

DESCENTE SPORTS SCIENCE Vol.6/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE