Simultaneous arterial (left atrial) and mixed venous (right atrial) blood samples were anaerobically drawn from 14 miniature swine (mean weight = 25.0 +/- 1.7 [SE] kg) in order to examine the adequacy of these animals as a model for the exercising human. Samples were drawn: 1) at rest; 2) during exercise that elicited 80.4 +/- 1.2% of the animals' measured maximal heart rates; 3) at exhaustion; and 4) during the 4th min of a standing, resting recovery period. At rest, the animals were mildly alkalotic (pHa = 7.497 +/- 0.016) and hypocapnic (pCO2a = 29.6 +/- 1.2 torr), with low hematological values (arterial hemoglobin = 6.66 +/- 0.18 mmol X 1-1; arterial hematocrit = 32.0 +/- 0.9%) and slightly elevated catecholamine concentrations. During the submaximal exercise, there were no statistically significant changes in the arterial blood pH or in plasma sodium (Na+) and chloride (Cl-) concentrations, with significant decreases observed in Hcta, pCO2a, and increases in arterial plasma norepinephrine, total protein, and potassium (K+) concentrations. At exhaustion, pHa and pCO2a decreased further, with increases noted in the arterial plasma concentrations of K+, epinephrine, total protein, and the Hct but not in Na+ or Cl-. During recovery, arterial lactate averaged 20.54 +/- 0.71 mmol X 1-1. Venous changes were similar to those observed in arterial blood, with a mean pHv of 7.168 +/- 0.043 and arterial lactate = 21.08 +/- 0.90 mmol X 1-1 during recovery. Exercise-induced hemoconcentration was similar for both arterial and venous sample sites during both the submaximal and exhaustive exercise.(ABSTRACT TRUNCATED AT 250 WORDS)