We studied the effects of the pericardium on diastolic left coronary pressure-flow relationships in heart-blocked and isolated canine preparations. In these preparations, the left and right coronary arteries were dilated with adenosine and perfused by means of a pressurized arterial reservoir. The diastolic left heart pressure (LHP) was controlled by the height of a reservoir connected to the left atrium and left ventricle. The right atrial and ventricular pressure i.e., coronary outflow pressure, was kept constant at 0 mm Hg. Before and after pericardiectomy, diastolic coronary pressure-flow relationships were obtained at three values of LHP (0, 15, and 30 mm Hg) with driving pressure decreasing (2 mm Hg/sec or less) from approximately 60 mm Hg to the actual zero-flow pressure (Pf = 0) during a single long diastole induced by cessation of ventricular pacing. The slopes of the coronary pressure-flow relationships were approximated by a linear regression analysis in which the correlation coefficients were greater than .98 in all cases. Before pericardiectomy, with LHP increasing from 0 to 15 and 30 mm Hg, the value of Pf = 0 significantly increased from 7 +/- 1 to 16 +/- 1 (p less than .01) and 28 +/- 2 mm Hg (p less than .01), respectively. After pericardiectomy, it increased from 7 +/- 1 to 14 +/- 1 (p less than .01) and 17 +/- 2 mm Hg (p less than .01), respectively. When LHP was at 0 and 15 mm Hg, the pericardiectomy had no effect on the value of Pf = 0.(ABSTRACT TRUNCATED AT 250 WORDS)