A doppler-echocardiographuc study of left ventricular hypertrophy and systolic functions was performed in 99 professional cyclists and 26 age, body surface and blood pressure-matched controls. The following T-mode echocardiographic parameters were determined: wall thickness and cavitary diameter, left ventricular mass (LVM), fibre shortening fraction (FSF) and ejection fraction (EF). The following doppler parameters were measured at the annulus (a) and tip (p) of the mitral valve leaflets: protodiastolic velocity peak (E), velocity peak during atrial systole (A) and A/E ratio. Compared with controls, the cyclists showed a significant increase of LVM (305 +/- 53 vs 174 +/- 41 g, p less than 0.0001) and of the h/R ratio of mean wall thickness (h) to cavitary radius (R) (0.40 +/- 0.04 vs 0.35 +/- 0.06, p less than 0.001). There was no significant difference between the two groups as regards FSF, EF and protodiastolic filling peak (E). In contrast, subjects in the cyclist group showed a significant increase of Ap (0.39 +/- 0.07 vs 0.47 +/- 0.09, p less than 0.001), Aa (0.36 +/- 0.07 vs 0.41 +/- 0.08, p less than 0.01) and A/Ep (0.54 +/- 0.12 vs 0.62 vs 0.62 +/- 0.11, p less than 0.0001). It is concluded that professional cyclists have an increase in size of their left ventricle and that repercussions of this enlargement on ventricular filling only appear during the atrial systole and are related to a slower heart rate.