Abstract: AIM:To investigate the genesis of arrhythmias and changes of density of β-AR, AC activity and cAMP level of myocardia in a stressed goat mode and to clarify the pathway of sympathetic signals across myocardial membrane. METHODS: Fifteen adult male goats were randomly divided into control, stress and metoprolol groups. Twenty four hour noise and flash light stimulation were used to establish the acute stress model and 24 h Holter monitoring was performed. Subsequently, animals were anesthetized and killed by bloodletting through the aorta, and myocardial tissues were kept for preparing membrane samples. β-AR density, AC activity and cAMP level were measured by radioligand binding assay and radioimmunoassay. RESULTS: Obvious stress responses occurred in stress and metoprolol groups. β-AR density increased similarly (P<0.05, P<0.01) in both groups and were higher than in control group (P<0.05, P<0.01). No significant difference was observed in KD values among the three groups. AC activity and cAMP level in stress group were higher than in control and metoprolol groups (P<0.05, P<0.01), and these indices in metoprolol group were also higher than in control group (P<0.05). CONCLUSION: Our study shows that intact β-AR-AC-cAMP pathway-mediated biological reactions result from sympathetic activation, and metoprolol may inhibit the signal transmitting pathway and partially block adverse effects of sympathetic activation.