Twenty dogs with patent ductus arteriosus occluded with Hemoclips were evaluated with a mean follow-up time of 799.4 days (range, 83 to 3,580 days). Significant decreases were found between pre- and postsurgical means for vertebral heart size and for echocardiographic left atrial/aortic-root ratios and percent fractional shortening (%FS). Despite a good clinical outcome, six of 20 dogs had persistent cardiomyopathy of overload with diminished %FS (28% or less) at follow-up. One dog had residual ductal flow identified five days postoperatively. Subsequent evaluations in this case at 60, 144, 226, 344, and 560 days postoperatively demonstrated gradually diminishing ductal flow. The remaining 19 dogs did not recanalize.