Background/Objectives: Myocardial infarction with non-obstructive coronary arteries (MINOCA) represents a heterogeneous clinical entity in which patients exhibit symptoms and biomarker evidence of myocardial infarction despite the absence of significant coronary stenosis. This study aimed to evaluate the diagnostic and follow-up value of left ventricular global longitudinal strain (LV-GLS) in patients with MINOCA and to investigate its association with inflammatory and glycemic biomarkers. Methods: A total of 287 patients presenting with acute coronary syndrome were prospectively enrolled. Based on coronary angiographic findings, patients were classified into two groups: myocardial infarction with obstructive coronary arteries (MIOCA; ≥50% stenosis, n = 237) and MINOCA (<50% stenosis, n = 50). In addition, an ischemic control group without obstructive disease (INOCA, n = 50) was included for comparative analysis. Laboratory tests, echocardiography, and LV-GLS were assessed at baseline and at 3 months. Results: Baseline left ventricular ejection fraction (LVEF) and LV-GLS were significantly lower in MIOCA compared with MINOCA (LVEF: 52.9 ± 10.3% vs. 59.7 ± 8.7%, p < 0.001; LV-GLS: −11.46 ± 4.84% vs. −12.63 ± 6.33%, p = 0.007, respectively). At 3 months, LVEF remained lower in the MIOCA group (57.5 ± 6.6% vs. 62.0 ± 7.9%; p < 0.001, respectively), whereas LV-GLS improved similarly in both groups with no significant difference (−15.27 ± 2.60% vs. −14.87 ± 5.21%; p = 0.29, respectively). Among MINOCA patients, the neutrophil-to-platelet ratio (NPR) (p = 0.017) and admission glucose (p = 0.047) were independently associated with impaired LV-GLS (defined as values greater than −16%). Conclusions: Although LVEF remained higher in MINOCA patients during follow-up, LV-GLS impairment persisted at levels comparable to those observed in MIOCA, suggesting ongoing subclinical myocardial dysfunction. LV-GLS offers superior diagnostic sensitivity to LVEF. Inflammatory and glycemic markers may aid in early risk stratification and guide management in patients with MINOCA.