Relationship between flow rates of cardiac lymph (LF), and coronary blood flow (CF), coronary perfusion pressure (PP), left ventricular peak systolic pressure (LVSP) and heart rate (HR) was studied in open-chest dogs. Intra-coronary administration of catecholamines (CA) and electrical stimulation of the cardiac sympathetic nerve (ES) increased LF transiently with a concomitant rise in the cardiac mechanical performance, while dipyridamole induced no change in LF in spite of a marked increase in CF. Isoproterenol at does of 0.3 and 3x10(8) g/kg induced an increasein LF to 119 +/- 4 and 167 +/- 20% (mean +/- SE); norepinephrine, 0.3 and 3 X 10(7) g/kg, to 118 +/- r and 141 +/- 13%; ES AT 5 and 20 Hz, to 135 +/- 11 and 167 +/- 10%, respectively. Peak responses of LF correlated with changes in LVSP (R = 0.59, N l1,P less than 0.001), CF Tr = 0.53, n = 51, P less than 0.001), PP (r = 0.49, n = 51, P less than 0.001) but not with changes in HR (r = 0.27, n = 51, 0.05 less than P less than 0.10). Cardiac pacing also showed a poor correlation between the changes in LF and HR under the same LVSP within the changes in HR up to 134% of control value (r = -0.12, n = 17, P GREATER THAN 0.50). It is concluded that LF is independent of changes in HR, and increased LF after CA or ES may be caused mainly by an augmented propulsive force.