Objectives: Little is known of the effect of pregnancy on canine cardiovascular function. This study was undertaken to evaluate the effect of pregnancy on canine echocardiographic variables. Animals, materials and methods: Serial echocardiographic examinations of 7 healthy, sexually intact female canine mongrels dogs that weighed between 9.7 and 13.4 kg were performed. The subjects were examined prior to ovulation, during early pregnancy, during late pregnancy within 6 days of parturition and again, after puppies were weaned. Results: Repeated measures ANOVA disclosed a statistically significant effect of time on end-systolic left ventricular dimension (LVIDs, p ΒΌ 0.005), left ventricular fractional shortening (%FS, p ΒΌ 0.001), Doppler-derived inflow and ejection velocities (all p < 0.05), as well as on heart rate (HR, p ΒΌ 0.03). %FS, HR, aortic ejection velocity, pulmonic ejection velocity and early diastolic mitral inflow velocity were maximal during late pregnancy. The increase in %FS resulted from a decrease in LVIDs. For Doppler-derived flow velocities, the range of differences of least square means (m/s) between early and late pregnancy was 0.21e0.32. Conclusions: While the magnitude of effect generally was small, this study provides evidence that pregnancy in healthy bitches is associated with changes in echocardiographic variables.