Objectives: This study quantifies cardiopulmonary bypass preparation artefacts on mean systemic arterial pressures (mAP), mean pulmonary arterial pressures (mPAP) and their ratio (mAP/mPAP) in order to assess the usefulness of this ratio as a pharmacodynamic marker for pharmacokinetic/pharmacodynamic modeling studies. Materials and Methods: Fifteen anesthetized swine were monitored every minute before initiation of cardiopulmonary bypass. Percent relative changes from pre-artefact values ( and #916;%) were used during anesthesia induction and stabilization ( and #916;% minute-1 reduction rates). In addition, in some animals, amplitude and duration were recorded for the following procedures: sternotomy, pulmonary artery catheter installation, purse-string sutures and cardiac cannulations. Results: Isoflurane 5% anesthesia induction effect on mAP, lasted on average 5.3+/-2.0 minutes at 5.9+/-1.9 and #916;% minute-1. Isoflurane 2% anesthesia stabilization effect on mAP lasted on average 36.0+/-8.0 min at 0.8+/-0.9 and #916;% minute-1. During stabilization, no change in mAP/mPAP was observed (p=0.68). Average amplitudes of artefacts on mAP were 30-50 and #916;%; almost twice those observed for mPAP and mAP/mPAP for the same manipulations (p<0.05). Pulmonary artery catheter installation artefacts lasted longer than those of other procedures (p<0.05). Average artefact duration was 4.5+/-2.5 minutes (n=160). Conclusions: In isoflurane-anesthetized swine, mAP/mPAP ratio remains constant during anesthesia stabilization, unlike mAP and mPAP individually. Moreover, the ratio shows potential as a pharmacodynamic biomarker for pharmacokinetic/pharmacodynamic studies involving CPB. [Arch Clin Exp Surg 2016; 5(1.000): 13-20]