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Purpose: The purpose of the present research was to investigate the effect of eight weeks of progressive resistance exercise and a subsequent detraining period on the indicators of muscle fiber shortening (FS%) and the relative wall thickness (RWT) of the left ventricle in low-mobility women. Method: This semi-experimental study was conducted in a field-laboratory setting. A total of 32 sedentary women, who met the criteria for participation and were able to engage in the exercise protocol, were randomly assigned to two groups: 1) Resistance training group (16 participants), and 2) Control group (16 participants). Anthropometric characteristics, body composition, and structural indices such as left ventricular muscle fiber shortening percentage (FS%) and relative wall thickness (RWT) were measured using an echocardiography device at three intervals: before the start of training, at the end of 8 weeks of training, and after a 4-week detraining period. The training protocol was implemented over 12 weeks, consisting of 8 weeks of training with three sessions per week, followed by 4 weeks of detraining. Data were analyzed using independent t-tests and repeated measures analysis of variance (ANOVA) at a significance level of p < 0.05, using SPSS version 21. Results: The results showed a significant difference in FS% between pre-test and post-test measurements for both the experimental and control groups (p < 0.05). Additionally, a significant decrease in FS% was observed in the training group during the detraining period (p < 0.05). Similarly, a significant change in RWT was found between pre-test and post-test measurements in both groups (p < 0.05), and significant changes in RWT were also observed during the detraining period in the training group (p < 0.05). Conclusion: Based on these findings, it can be concluded that 8 weeks of resistance training led to beneficial changes in the structure and function of the heart in sedentary women. However, the 4-week detraining period resulted in negative effects on these adaptations. Therefore, it is recommended that individuals engage in regular and structured resistance training to maintain these positive adaptations.