Objective To demonstrate the myocardial lesion associated with long-term administration of methamphetamine in rats. Methods The experimental models of intoxication of methamphetamine were established in Sprague-Dawley rats. Methamphetamine hydrochloride （3 mg·kg-1·d-1） was subcutaneously injected to rats in methamphetamine-treated group （n = 16）

and normal saline at the same dose was injected to rats in control group （n = 16）. After 1 week and 8 weeks of injection

8 rats in each group were sacrificed and their hearts were examined with light microscopy and electron microscopy

respectively. Results After 1 week of methamphetamine exposure

foci of contraction band and cellular degeneration were present in subendocardial myocardium. Cellular degeneration

myocytolysis

and contraction band necrosis became prominent and extensive in methamphetamine-treated rats after 8 weeks. Hypertrophy

intracellular vacuolization

and fibrosis were also observed. The ultrastructural feature showed marked swelling and degeneration of mitochondria

enlargement of sarcoplasmic reticulum

and dissolution of myofilaments. No obvious cardiac myocyte lesions were observed in rats of control group. Conclusion Methamphetamine abuse daily for a long time may result in an increased risk of cardiovascular lesions similar to cardiomyopathy.