Objective To study the effects of different doses of isoproterenol ( ISO) on cardiac function and pathological morphology in rats. Methods Sprague-Dawley rats were randomly divided into Control, low-dose model (ISO 25 mg / kg), medium-dose model (ISO 50 mg / kg), and high-dose model (ISO 100 mg / kg) groups. In the model group, different doses of ISO were injected subcutaneously at multiple points in the neck for two consecutive days whereas the Control group received the same volume of saline. Changes in heart rate, QRS interval, duration and amplitude of P-waves were detected by electrocardiogram (ECG). The myocardial infarct size was detected by TTC staining and the pathological morphology of myocardial tissues was observed by HE staining 24 hours after the last administration. Results Compared with the Control group, the heart and left ventricular weights of rats in different dose model groups were significantly increased (P< 0. 01) and the ECG of rats showed that the P-wave duration in the high-dose model group was increased (P< 0.01), the P-wave amplitude in the low-dose and high-dose model groups was increased (P< 0.05, P< 0.01, respectively) and arrhythmia was present. TTC staining and HE staining showed pathological changes related to myocardial injury. Conclusions Different degrees of damage were observed in myocardial tissues of the model groups and the most serious myocardial injury was observed in the high-dose model group. This study provides a basis for animal model development and research of the mechanisms of ischemic / infarct heart disease.