Melatonin is a stress combating drug for dogs that reduces the anxiety levels felt by them, and an over-the-counter remedy that can be used to treat mild anxiety in dogs and it is a much better alternative to using tranquilizers in situations where your dog may get het up, such. So in this study we decided to survey the electrocardiogram induced change by melatonin in dog heart. In this study (experimental - intervention), 10 male dogs randomly selected and were tested. Then, animals were received the oral dose of melatonin products (3 mg /Dog/daily). And, at times zero (before drug administration), and one month after drug administration, electrocardiogram in lead II was recorded. After recording electrocardiogram, heart rate and other factors Including PR interval, RR interval, QT interval, ST segment changes were analyzed. All of the electrocardiogram driven data were analyzed by, T tests. Decreasing of heart rate statistically was significant (p<0.05).We observed, also P amplitude (P amplitude) was significantly decreased (p<0.05). Indeed we did not found any significant data about QT interval. In this study we observed that melatonin can induce bradycardia and decrease the heart rate , it shows that melatonin act as negative chronotrope agent in dog .Unfortunately in animal and dog we did not found similar study, but Similar data was found in human. so it will be very useful for small animal clinicians and internists for controlling of atrial and sino-atrial tachycardia and atrial fibrillations. We recommend more investigation of melatonin on dog heart echocardiogram and in holter monitoring associated with dog hypertension.
