Regional pressure-flow relationships within the right coronary artery (RCA) circulation of swine were determined. Enflurane-anaesthetized swine (n = 7) were studied during step-wise reductions of RCA perfusion pressure using an extracorporeal circuit. Regional blood flow was measured using microspheres and contractile function of the right ventricle was measured using sonomicrometry. The RCA perfusion territory was divided into its anatomic components: right ventricular free wall (RV), interventricular septum (with further division in transmural thirds; SEP-LV, SEP-MID and SEP-RV) and right atrium (RA). Pressure-flow relations were constructed for each region and autoregulatory capacity assessed through calculation of an autoregulatory index (AI, closed-loop gain). The pressure-flow relationship for the entire RCA exhibited autoregulation down to a pressure of 40 mmHg. The SEP-LV exhibited a similar relationship with loss of autoregulation at approximately 40 mmHg. The pressure-flow relationship of the RV, however, showed autoregulation to a pressure of 30 mmHg with a decrease of blood flow only at a pressure of 20 mmHg. Little autoregulation was observed in the RA. Autoregulatory gain assessed by AI was similar in RV, SEP-LV and SEP-RV as pressure was reduced from 90 to 55 mmHg (RV = 0.54 +/- 0.41; SEP-LV = 0.58 +/- 0.36; SEP-RV = 0.83 +/- 0.36). With further reductions of pressure, AI was highest in the RV, followed by the SEP-RV and then SEP-LV.(ABSTRACT TRUNCATED AT 250 WORDS)