Electrocardiographic observations on the tuatara, Sphenodon punctatus

1. 1. Electrocardiograms were obtained from two unrestrained tuataras at body temperatures from 7 to 26°C. 2. 2. Heart rates were lower than previously reported for resting Sphenodon, but were similar to resting rates of large lizards. 3. 3. EGG intervals (P–R, R–T, P i –T f ) did not differ greatly from those of Iguana iguana, except that duration of ventricular depolarization was more sensitive to temperature in Sphenodon. 4. 4. In general, the electrocardiology of Sphenodon closely resembles that of squamate reptiles. 5. 5. An unusual feature was an occasional increase in the absolute duration of R–T when heart rate increased slightly in response to disturbance.