Objective To investigate the effects of spontaneous agonal respiration on coronary perfusion pressure (CPP) during untreated cardiac arrest (ventricular fibrillation) in swine model.Methods Ten male healthy domestic swines (25.0 ± 1.5) kg were anaesthetised,intubated and mechanically ventilated.The catheterizations were separately inserted into the right atrium and thoracic aorta to monitor aortic pressure (AOP) and right atrial pressure (RAP).A pacing electrode was inserted into the right ventricle to induce ventricular fibrillation (VF).VF was induced by intra-ventricular stimulation withalternating electric current and untreated for 8 minutes.AOP and RAP were recorded until respiratory activity ceased.The CPP before and after agonal respiration was calculated and analyzed by paired-sample T test.Results All animals presented with agonal respiration from 1 to 6 minutes after VF during the first attempt.The CPP was (7.18 ±4.22) mmHg at 1 sec before agonal respiration,(11.78 ±5.16) mmHg at 0 sec after agonal respiration,(8.75 t:4.38) mmHg at 5 sec after agonal respiration and (8.23 ± 4.55)mmHg at 6 sec after agonal respiration.The CPP at 0 sec after agonal respiration was higher than that before agonal respiration (t =-3.140,P =0.012).The CPP at 5 sec after agonal respiration was higher than that at 1 sec before agonal respiration (t =-2.828,P =0.020).There was no difference in CPP between at 6 sec after agonal respiration and at 1 sec before agonal respiration (t =-1.778,P =0.109).Conclusions Agonal respiration accompanies ventricular fibrillation.After agonal respiration,the coronary perfusion pressure is increased for 5 seconds being in favor of cardiaopulmonary resuscitation.