background: tramadol is a centrally acting analgesic, whose mechanism of action involves opioid-receptor activation. previously, we have shown that tramadol and its enantiomers had a negative inotropic effect on the papillary muscle in which the (+)-enantiomer is more potent than (-)- and (±)-tramadol. objective: in this study, we investigated the effects of tramadol and its enantiomers on l-type calcium current (ica-l). results: tramadol (200 μm) reduced the peak amplitude of ica-l at potentials from 0 to +50 mv. at 0 mv, ica-l was reduced by 33.7 ± 7.2%. (+)- and (-)-tramadol (200 μm) produced a similar inhibition of ica-l, in which the peak amplitude was reduced by 64.4 ± 2.8% and 68.9 ± 5.8%, respectively at 0 mv (p > 0.05). tramadol, (+)- and (-)-tramadol shifted the steady-state inactivation of ica-l to more negative membrane potentials. also, tramadol and (+)-tramadol markedly shifted the time-dependent recovery curve of ica-l to the right and slowed down the recovery of ica-l from inactivation. the time constant was increased from 175.6 ± 18.6 to 305.0 ± 32.9 ms (p < 0.01) for tramadol and from 248.1 ± 28.1 ms to 359.0 ± 23.8 ms (p < 0.05) for (+)-tramadol. the agonist of μ-opioid receptor damgo had no effect on the ica-l. conclusion: the inhibition of ica-l induced by tramadol and its enantiomers was unrelated to the activation of opioid receptors and could explain, at least in part, their negative cardiac inotropic effect.