The impact of prolonged exercise upon right ventricular (RV) function is poorly understood and to date no studies have utilized tissue-Doppler imaging (TDI). Thirty-five marathon runners (age range 18–50 years) volunteered for the study. Two-dimensional, pulsed Doppler, and TDI studies were performed one day before and immediately following race completion. Right and left ventricular (LV) longitudinal TDI myocardial velocities were acquired from the tricuspid annulus and mitral annulus, providing velocity data during systole (S′), early diastole (E′), and late diastole (A′). Transtricuspid and transmitral, early diastolic (E), and late diastolic (A) velocities and ratios were assessed using conventional pulsed-wave Doppler. RV and LV fractional area changes (FAC) were calculated from RV and LV end-diastolic and end-systolic areas recorded from 2D scans in a subsample (n = 23). RV myocardial velocities were unchanged pre-post race in S′ (21.1 ± 2.7 to 21.7 ± 4.5 cm s−1, P > 0.05), reduced in E′ (23.3 ± 3.5 to 19.9 ± 5.3 cm s−1, P < 0.05), increased in A′ (19.1 ± 3.6 to 23.7 ± 6.8 cm s−1, P < 0.05) with a resultant decline in E′/A′ (1.28 ± 0.36 to 0.94 ± 0.45, P < 0.05). This pattern of data was mirrored in the LV. Similarly both pulsed-Doppler tricuspid and mitral E/A ratios decreased from pre- to postrace (P < 0.05). FAC for the RV and LV were unaltered postrace (P > 0.05). The impact of differing age, finishing time (173–330 min), hemodynamic loading and heart rate upon RV and LV function pre- to postrace was negligible. In conclusion, TDI and 2D data, for both the RV and LV demonstrated little change in systolic function after a marathon race. Conversely, a reduction in diastolic function was observed in both ventricles for which a mechanism has yet to be deduced.