Azadirachta indica commonly referred to as “Dogonyaro” in Nigeria has been reported to have several beneficial and medicinal properties. The plant has been used traditionally for the treatment of gastrointestinal diseases and it has also shown great potential as remedy for blood parasite infections including trypanosomiasis and malaria. There is however a dearth of information on the cardiac effect of this plant. This study was conducted to evaluate the possible effects of the ethanolic extract of A. indica leaves on the electrocardiogram of dogs.Twenty Nigerian local dogs, obtained from a local dog breeding facility were divided into 4 groups of 5 dogs each. Group A was the control and were administered only water orally while groups B, C, and D were orally administered 50mg/kg, 100mg/kg and 200mg/kg respectively of the ethanolic extract of the leaves of A. indica for a period of 7 days. Lead II ECGs were recorded without anesthesis and analyzed prior to the administration of the extract and also at the termination of the experiment on day on day 7. Data were analyzed using ANOVA at 5% level of significance.After 7 days of administration, Group C dogs had statistically signicantly higher (p<0.05) increase in P-R interval value. Also, there was a statistically significant (p<0.05) increase in the values of the QTc Fridericia in both group B and C dogs. Mean R-wave amplitude value was significantly (p<0.05) lower in group D dogs.The use of A. indica should be with great caution as prolonged administration could have adverse effects on the heart.