Several studies have found 2-dimensional echocardiography and conventional spectral Doppler ultrasound useful in the assessment of ventricular septal defect (VSD), but few data exist regarding the usefulness of color Doppler flow imaging in evaluating this problem. Thus, the results of color flow imaging performed in 14 patients who presented with a recent acute myocardial infarction (AMI), hemodynamic instability and a new systolic murmur were evaluated. All patients underwent cardiac catheterization for definitive diagnosis, which proved to be VSD in 7 and acute mitral regurgitation in 7. VSD, identified by turbulent flow traversing the ventricular septum during ventricular systole, was correctly identified in all 7 patients with septal rupture. In the remaining 7 patients with a new murmur after AMI, mitral regurgitation was demonstrated as turbulent systolic flow in the left atrium by both color flow imaging and cine ventriculography. In all 14 patients with new murmurs, color flow imaging was 100% accurate for the presence or absence of VSD. Color flow imaging localized the septal defect to the apical septum (3), inferior septum (3) or both inferior and apical septal regions (1), and was 100% concordant for location compared with cineangiography, surgery and conventional Doppler echocardiographic techniques. Color flow imaging was accurate in identifying the presence and location of VSD complicating AMI, and accurately differentiated VSD from mitral regurgitation. Color flow imaging provides safe, rapid diagnosis of VSD complicating AMI, and may alleviate the need for diagnostic right-sided heart catheterization and preoperative cine ventriculography in these seriously ill patients.