['The purpose of the study was to assess the dynamic changes in left ventricular (LV) volume by transthoracic three-dimensional echocardiography (3DE) and to compare the results with those obtained by magnetic resonance imaging (MRI).', 'Thirty healthy children were studied by digitized 3DE and Doppler, and by MRI. Three-dimensional echocardiography of LV was performed by using rotational acquisition from the transthoracic apical view with ECG gating and without respiratory gating. The acquisition of 3DE data took 10-15s. Three-dimensional echocardiography gave similar values to MRI for EDV, ESV and LVM measurements, and the results correlated well. Peak emptying rates by 3DE and MRI were -236.6 and -169.6ml/s and peak filling rates were 215.0 and 215.9ml/s, respectively. Dynamic changes of LV volumes during the heart cycle were detectable with both methods.'] Is transthoracic three-dimensional echocardiography as good as magnetic resonance imaging in measuring dynamic changes in left ventricular volume during the heart cycle in children?