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Effects of hexametazidine [1

4-di（2

3

4-trimethoxybenzyl）piperazine]on the physiological properties of guinea-pig papillary muscles were investigated.Hexametazidine possesses a concentration-dependent negative inotropic effect(IC

50

=81.8±16.9μmol/L).The effect of hexametazidine（30.8μmol/L）was antago-nized completely by increasing the concentration of Ca

2+

from 1.8 to 5.4mmol/L.Hexametazidine（30.8μmol/L）increased the threshold concentration of adrenalinefor inducing the automaticity of the muscles from 3.95±1.80 to 6.67±4.84μmol/L（P

<

0.05）.It prolonged the functional refractory period from 218±14 to 254±20ms（P

<

0.05）at the concentration of 61.6μmol/L.Hexametazidine（6.2μmol/L）antago-nized the positive inotropic effect of isoprenaline competitively and ofhistamine non-competitively（pA 2 and pD2′ values were 5.45 and 4.13

respectively）.