Doppler myocardial imaging is a new cardiac ultrasound technique based on the principles of colour Doppler imaging which can determine myocardial velocities by detecting the changes of phase-shift of the ultrasound signal returning directly from the myocardium. To determine the normal range of transmural velocities in healthy hearts a prospective study was carried out involving 42 normal subjects (age from 21 to 78, mean 47 +/- 16 years). Using M-mode Doppler myocardial imaging the peak values of the mean velocity and velocity gradient across the left ventricular posterior wall were measured during standardized phases of the cardiac cycle. Peak mean velocities had the following values during the cardiac cycle: isovolumic contraction - 1.3 +/- 1.2 cm. s-1, early ventricular ejection 4.2 +/- 1.2 cm. s-1, late ventricular ejection 1.8 +/- 1.1 cm. s-1, isovolumic relaxation -2.0 +/- 0.8 cm. s-1, rapid ventricular filling -6.6 +/- 2.2 cm. s-1, atrial contraction -2.8 +/- 1.8 cm. s-1, atrial relaxation 1.2 +/- 1.1 cm. s-1. Peak velocity gradients were: isovolumic contraction 1.3 +/- 1.9 s-1, early ventricular contraction 4.7 +/- 1.9 s-1, late ventricular contraction 1.1 +/- 1.0 s-1, isovolumic relaxation -0.6 +/- 0.5 s-1, rapid ventricular filling 6.1 +/- 3.4 s-1, atrial contraction 2.6 +/- 1.7 s-1, atrial relaxation 0.0 +/- 0.3 s-1. Linear regression analysis showed that with the increase of age, peak velocity gradient decreases during rapid ventricular filling (r = 0.83; P < 0.0001) and increases during atrial contraction (r = 0.86; P < 0.0001) while peak mean velocity increases only during atrial contraction (r = 0.80, P < 0.0001). Thus, there was no correlation between increasing age and systolic peak mean velocity and peak velocity gradient but both diastolic filling phases rapid ventricular filling and atrial contraction demonstrated age-related changes. In summary, this study has determined the age-related range of normal transmural myocardial velocities within the left ventricular posterior wall in healthy hearts during the cardiac cycle. We conclude that these measurements of peak mean velocities and peak velocity gradients, should form the baseline for subsequent Doppler myocardial imaging clinical studies on myocardial diseases processes.