A Doppler index of myocardial performance (IMP) has been recently proposed in human cardiology, which is calculated from the isovolumic contraction time (ICT), isovolumic relaxation time (IRT), and the ejection time (ET) using the following formula: (ICT+IRT)/ET. In this study, IMP was measured and evaluated in Newfoundland dogs categorized in four groups: Normal dogs (n = 31), dilated cardiomyopathy (DCM) (n = 34), depressed fractional shortening (dFS) (n = 27), and left ventricular enlargement (LVE) (n = 7). IMP was found to be independent of age, sex, body surface area, and the R-R interval in the Normal group. There were significant differences in IMP between the DCM group and the Normal and dFS groups (P < 0.05) and between Newfoundlands with overt vs. occult DCM. IMP is a Doppler index which appears to correlate with severity of disease and may be of use in the early diagnosis of affected dogs during screening for the presence of DCM.