Background: Patients may experience a decline in cardiac function even after successful percutaneous coronary intervention (PCI). It is apparent that the assessment of left ventricular (LV) function before PCI is often overlooked. The purpose of this review is to explore the significance of LV function assessment before PCI by comparing the differences in short- and long-term PCI outcomes between patients with different LV ejection fraction (LVEF) stratified preoperatively. Methods: PubMed and Scopus were searched to identify potential studies from January 1, 2001 through January 1, 2022. Results: A total of 969,868 participants in 33 studies at different stratifications of baseline LVEF were included in this review and their PCI outcomes were stratified for analysis. The hazard ratio of all-cause mortality within 30 days, one year and greater than 1 year after PCI between patients with abnormal and normal LVEF were 2.96 [95% CI, 2.2, 3.98], 3.14 [95% CI, 1.64, 6.01] and 3.08 [95% CI, 2.6, 3.64]; moderately impaired LV function versus normal were 2.32 [95% CI, 1.85, 2.91], 2.04 [95% CI, 1.37, 3.03], 1.93 [95% CI, 1.54, 2.44]; poor LV function versus normal were 4.84 [95% CI, 3.83, 6.1], 4.48 [95% CI, 1.37, 14.68], 6.59 [95% CI, 4.23, 10.27]. Conclusions: A moderate or severe reduction in patients’ LVEF may have a serious impact on PCI prognosis. We strongly advocate for adequate assessment of LVEF before PCI as this will assist in choosing the optimal revascularization and postoperative treatment, thereby reducing short- and long-term mortality.