Background: Diuretics can induce thiamine deficiency which develops cardiac failure. This study aimed to examine the effect of chronic administration of thiamine and furosemide, as a most commonly used diuretic, on the mechanical activity of heart in the isolated rat heart.

Materials and Methods: In this experimental study, rats were divided into three groups (n=8 for each group): the control group (C) received no drug, the furosemide group (FUR) received furosemide (2 mg/Kg) daily for 53 days and the furosemide+thiamine group (FUR+THI) received furosemide (2 mg/Kg)+thiamine (70 mg/kg) daily for 53 days via drinking water. At the end of the experiment, using isolated heart, heart rate and mechanical activity were recorded during baseline and at 1 (EP1) and 5 (EP5) minutes after the addition of epinephrine to the bath.

Results: Heart contractility was increased in the FUR+THI group compared to the FUR and C groups at baseline and EP1. Moreover, contractility in the FUR+THI group was higher than the C group at Ep5. Contraction velocity and heart rate were increased at all three points in FUR+THI group compared to the C and FUR groups, while contraction velocity in FUR group only at EP1 and EP5 was significantly higher than the C group. Heart rate in FUR+THI group was higher than the C and FUR groups at all three points heart rate in FUR group at baseline was significantly higher than the C group.

Conclusion: Co-administration of thiamine and furosemide has positive inotropic and chronotropic effects on the isolated heart, but the possible mechanisms for these effects need further research.