Introduction: Obesity is a major risk factor for type 2 diabetes mellitus. Cardiovascular disease is the major cause of morbidity in diabetic patients. The electro-mechanical function of the heart is frequently compromised in diabetic heart. Few studies have investigated the effects of obesity and obesity/diabetes (diabesity) on the electrical conduction system of the heart.                                                                  Aims & Objectives: In vivo biotelemetry techniques were used to evaluate the effects of obesity and diabesity on the electrical conduction system of the heart in the Zucker lean (ZL), Zucker fatty (ZF) and Zucker diabetic fatty (ZDF) rat.   Methods: Experiments were performed in ZL, ZF and ZDF rats (Charles River, UK). Heart biopotential, physical activity and body temperature were monitored using an in vivo biotelemetry system (Data Sciences, USA). The transmitter devices were surgically implanted in 30 rats (10 ZL, 10 ZF, 10 ZDF) aged 75 days under general anesthesia. The transmitter devices were inserted into the peritoneal cavity and the electrodes from the devices were arranged in Einthoven Lead II configuration (right foreleg and left hindleg). Data recording was continued for a period of 4 months. Data are presented as mean ± SEM. Statistical analysis was performed using Two way repeated measures ANOVA and Independent and Paired samples t Test as appropriate. Ethical approval for the project was obtained from the Animal Research Ethics Committee, UAE University.   Results: At the end of the biotelemetry experiments ZL, ZF and ZDF rats body weights were (429.0±16.0 g, n=11), (725.3±18.5 g, n=12) and (608.6±45.8 g, n=13), respectively and fasting blood glucose values were (92.3±2.2 mg/dl, n=15), (131.3±3.8 mg/dl, n=16) and (208.3±13.9 mg/dl, n=16), respectively. Heart rates (HRs) were significantly (p0.05) differences in HRV at low frequencies, reduced HRV at high frequencies and increased sympathovagal balance in ZDF compared to ZF and ZL rats.   Conclusions: HR was reduced by aging and additionally reduced by diabesity in the absence of changes in physical activity and body temperature. Reductions in HRV associated with altered sympathovagal drive might partly underlie disturbed HR in the ZDF rat.