Pulmonary venous flow was recorded by transthoracic pulsed Doppler echocardiography in 10 endurance trained male athletes and in 10 age matched sedentary male controls. The ratio of peak systolic (S) to peak diastolic (D) flow velocity was much lower in athletes than in controls (0.8 +/- 0.22 vs. 1.13 +/- 0.37 p < 0.05). 5 out of 10 athletes had values less than 0.82 which was the lowest value in the control group. Athletes also hat significantly higher mitral flow E/A ratios and lower heart rates. Physical fitness caused by endurance training should be acknowledged one of the causes for an abnormally low S/D ratio.