Streptozotocin (STZ)-induced diabetic cardiomyopathy is frequently associated with altered heart rhythm. The effects of insulin treatment on heart rhythm were investigated using biotelemetry techniques. Transmitter devices were surgically implanted in the peritoneal cavity of young adult male Wistar rats. Electrodes from the transmitter were arranged in Einthoven bipolar, Lead II configuration. ECG, physical activity and body temperature data were recorded for 10 days before STZ treatment, for 20 days following administration of STZ (60 mg/kg) and thereafter, for 30 days whilst rats received daily insulin. Heart rate, heart rate variability, physical activity and body temperature declined rapidly 3 - 5 days after administration of STZ. Pre-STZ heart rate was 362±7 beats per minute, falling to 266±12 beats per minute 5–15 days after STZ with significant recovery to 303±14 beats per minute 10–20 days after commencement of insulin. There was significant recovery of body temperature however, there was no significant recovery in heart rate variability or physical activity during insulin replacement. Defective autonomic regulation and/or mechanisms of control that are intrinsic to the heart may underlie disturbances in heart rhythm in STZ-induced diabetic rat.