Objective To explore the effect and safety of calcium dibutyryl adenosine cyclophosphate(dbcAMP-Ca)combined with metoprolol in the treatment of older adults with heart failure combined with arrhythmia.Methods A total of 102 elderly patients with heart failure combined with arrhythmia were enrolled in our hospital between February 2021 and April 2023.The list of patients enrolled was entered into a random database by independent staffs not involved in the study and random assignment sequences were generated by the SAS9.4 software.Then,the 102 elderly patients were divided into a control group(n=51)and an experimental group(n=51).Patients in the control group were given metoprolol at an initial dose of 6.25 mg/d,which was gradually increased to the target dose of 25 mg/d.Patients in the experimental group were given 40 mg of dbcAMP-Ca once a day via intravenous drip in addition to the treatment given to the control group.Both groups were treated for 4 weeks.The rate of effective response to clinical treatment(the number of cases achieving significant effects and those achieving some effects divided by the total number of cases in the group)was defined as the main outcome index.Secondary indexes included cardiac function,heart rate variability,exercise ability,hemorheology,myocardial injury indexes,inflammatory indexes,and the occurrence of adverse reactions.Results The rate of effective response to clinical treatment was higher in the experimental group than that in the control group(94.12%[48/51]vs.78.43%[40/51],P<0.05).After treatment,the left ventricular end-diastolic and end-systolic dimensions(LVEDD and LVESD)and the interventricular septal thickness(IVS)were lower in the experimental group than those in the control group,while the left ventricular ejection fraction(LVEF)and the stroke volume(SV)were higher in the experimental group than those in the control group(P<0.05).In terms of heart rate variability after treatment,the standard deviation of all the normal-to-normal intervals/the average of all the normal-to-normal intervals(SDNN/SDANN),the percentage of NN50 in the total number of normal-to-normal intervals(PNN50% ),and the root mean square of the differences between adjacent normal-to-normal intervals/root mean square differences of successive R-R intervals(RMSSD)were higher in the experimental group than those in the control group(P<0.05).In terms of exercise capacity after treatment,the subjects in the experimental group covered more distance in the 6-min walk test than those in the control group did(P<0.05).In terms of the hemorheology indexes after treatment,the levels of platelet aggregation rate(PAgT),fibrinogen(FIB),erythrocyte sedimentation rate(ESR),and whole blood viscosity(ηb)were lower in the experimental group than those in the control group(P<0.05).In terms of the myocardial injury indexes after treatment,the levels of serum N-terminal pro-brain natriuretic peptide(NT-pro BNP)and cardiac troponin I(cTnI)were lower in the experimental group than those in the control group,while the levels of insulin-like growth factor 1(IGF-1)and cardiotrophin 1(CT-1)were higher in the experimental group than those in the control group(P<0.05).In terms of the inflammatory indexes after treatment,the levels of interleukin-6(IL-6),high-sensitive C-reactive protein(hs-CRP),and tumor necrosis factor-α(TNF-α)were lower in the experimental group than those in the control group(P<0.05).The incidence of adverse reactions in the experimental group(9.80% )and that in the control group(7.84% )were comparable(P>0.05).Conclusion The use of dbcAMP-Ca in addition to metoprolol can effectively improve cardiac function,heart rate variability,and exercise tolerance,while inhibiting inflammatory response in elderly patients with heart failure combined with arrhythmia,with high medication safety.The combination medication shows better safety and therapeutic effects than those of metoprolol used alone.