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 openchest (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.