<p>The second-to-fourth digit ratio (2D:4D) has been explored as a marker of prenatal hormonal exposure, but its association with left main coronary artery (LMCA) stenosis, particularly in women, remains unclear. This prospective observational study included 400 patients undergoing coronary angiography and cardiac surgery. Right- and left-hand 2D:4D ratios were measured, and LMCA stenosis was assessed angiographically. Exploratory analyses evaluated potential associations between right-hand 2D:4D ratios and selected postoperative outcomes, including intensive care unit length of stay and acute kidney injury. Female patients were further stratified according to LMCA stenosis (&lt; 50% vs. ≥ 50%), and multivariable logistic regression analysis was performed. Among female patients, right-hand 2D:4D ratios were significantly higher in those with LMCA stenosis ≥ 50% compared with those with &lt; 50% stenosis, whereas no significant association was observed for left-hand 2D:4D ratios. In penalized multivariable regression analysis, the right-hand 2D:4D ratio remained independently associated with significant LMCA stenosis in female patients. No clinically meaningful associations were identified between right-hand 2D:4D ratios and selected postoperative outcomes in either sex. However, given the small number of events, these findings should be interpreted as exploratory and hypothesis-generating. These findings suggest a potential sex-specific association between prenatal hormonal markers and LMCA disease severity in women. Further validation in larger cohorts is required.</p>