During vigorous exercise, the cardiac output of an athlete will be much higher than that of an ordinary man. This is due to

Due to ventricular hypertrophy, the stroke volume of athletes is higher than normal people. During rest, their heart rate is lower(resting bradycardia). Still, their cardiac output will be normal because of higher stroke volume. During exercise, their heart rate increases and stroke volume is higher. Due to this, the cardiac output will be much higher (Cardiac output = Stroke volume x Heart rate).