3,4,5-Trihydroxystibene-3-beta-mono-D-glucoside (PD) from Polygonum cuspidatum 0.05-0.45 mmol/L increased beat rate of myocardial cells from 100% to 112-220%. This action of PD 0.15 mmol/L was agonized by nisoldipine 0.1, propranolol 10 and phentolamine 1 mumol/L. PD (0.05, 0.15 mmol/L) decreased the lactate dehydrogenase (LDH) amount liberated by myocardial cells, from 98 +/- 11 IU/ml of deprivation of oxygen and glucose (DOG) to 55 +/- 16, 68 +/- 14 IU/ml (P less than 0.01) 6 h after injury of DOG; 77 +/- 9, 80 +/- 6 IU/ml (P less than 0.01) 9 h after injury of DOG. PD 0.15 mmol/L decreased the LDH amount liberated by myocardial cells, from 311 +/- 34 to 231 +/- 42 IU/ml (P less than 0.05) 9 h after injury of chlorpromazine (CPZ). It is suggested that PD can protect myocardial cells injured by DOG and CPZ.