Hemodynamic, respiratory, and cerebral variables during 2 h of standard external CPR were studied in 5 dogs. In an additional 12 dogs, possible augmentation of these variables by Military Anti-Shock Trousers (MAST) was evaluated. In 9 dogs, external and internal cardiac massage were compared. During ventricular fibrillation (VF) and after 2 min of circulatory arrest, standard CPR basic life support (without drug support) could sustain only borderline values: systolic arterial pressure (SAP) remained at 70--80 mm Hg and mean arterial pressure (MAP) at 35--45 mm Hg. Sternal compressions increased central venous pressure (CVP) to near SAP, and also increased intracranial pressure (ICP), but less than CVP. Thus, systemic perfusion pressures (SPP, i.e., MAP-mean CVP) control value 130 mm Hg) were only 11--15 mm Hg; and cerebral perfusion pressures (CPP, i.e., MAP-ICP) were 20--32 mm Hg during CPR. Common carotid arterial blood flow (CCABF) remained at an average of 8--20% of control values. Normalization of aerobic metabolism proved impossible (final pHa of 7.1). During external CPR, MAST inflation moderately increased MAP, SAP, SPP, and CPP; and significantly increased CCABF from 6.8 to 13.2% of prearrest control. The MAST failed to improve cerebral venous PO2, pupil signs, and EEG activity. With fixed pressure IPPV/100% O2, the MAST decreased tidal volumes and PaO2 (increased shunting); and increased PaCO2 and acidemia. Epinephrine 1 mg iv improved arterial pressures but not flows. A switch to open-chest (internal) cardiac massage (OCCM) after 2 h of external CPR significantly increased arterial and perfusion pressures (decreased venous pressures) and more than doubled CCABF; and resulted in a return of EEG activity and pupillary constriction. Prolonged standard CPR, and to a lesser extent MAST-augmented CPR, seem unlikely to maintain adequate oxygen transport for vital organ systems viability, particularly the brain. OCCM might better sustain viability.