In this study, we aimed to investigate the effects of cumulative doses of Zn2+ (by exposing samples to 1 µM, 10 µM, and 100 µM ZnCl2) on myocardial papillary muscle contractions isolated from rat hearts in vitro and the roles of the zinc finger protein ZEB1 in this effect. In these preparations, 100 µM ZnCl2 application in different protocols caused a decrease in contraction force and an increase in contraction time in both frequency-dependent parameters and pre-expected stimuli when compared to the control group. Our study data show that Ca2+ homeostasis is closely related to increasing Zn2+ doses (especially at 100 µM ZnCl2 dose). Secondly, the levels of ZEB1, a zinc finger protein, were also significantly lower in the 100 µM ZnCl2 group compared to the other groups, which seems to be related to the increase in Ca2+ that triggers ROS production at high doses of Zn2+. The data of our study, which we conducted to understand the Zn2+ concentrations in the heart and to reveal new mechanisms that play a role in the regulation of Ca2+ dynamics in heart tissue and is the first research in the literature on this subject, show that in vitro zinc application may have a dose-dependent effect on myocardial papillary muscle contractions.