Right bundle-branch block in a dog.

A cardiac gallop rhythm and a low-grade systolic murmur were found in an 8-year-old Miniature Poodle. Conditions had not changed 7 months later, but electrocardiographic evaluation revealed a short R wave, large S wave, prolonged QRS interval and mean electrical axis of -100 degrees, all consistent with a right bundle-branch block. The dog has remained in good condition for 2 years without right-heart enlargement, ectopic beats or tachycardia, indicating the condition was an incidental finding.