Recently the maximal early diastolic velocity in long-axis direction of the right ventricle (RV) obtained by tissue Doppler imaging (MDV TDI) has been introduced in the assessment of RV diastolic function (RVDF). There are reasons to think that also the maximal early diastolic velocity in long-axis direction of the RV obtained using M-mode echocardiography (MDV TAM) could be used to assess RVDF. Therefore, 29 patients were examined with echocardiography and MDV TAM and MDV TDI were measured and compared. A good correlation (r = 0.76, P < 0.001) was found between MDV TAM and MDV TDI indicating that MDV TAM might be used in the assessment of RVDF. However, the velocities obtained by MDV TDI (126.7 +/- 38.9 mm s(-1)) were significantly (P < 0.001) higher than the velocities obtained by MDV TAM (78.3 +/- 27.8 mm s(-1)) and the agreement between MDV TAM and MDV TDI was rather poor probably mainly due to differences in the measuring technique. This means that reference values cannot be used interchangeably between MDV TAM and MDV TDI. If MDV TAM is going to be used in the assessment of RVDF new reference values have to be produced if today's technique and recommendations to measure MDV TAM and MDV TDI are used. However, as most new echocardiographs are equipped with PW-TDI technology it seems preferable to use this technique and compare obtained values with already established reference values.