Background: Non-ST Segment Elevation Acute Coronary Syndrome (NSTE-ACS) patients often present with complex cardiac pathophysiology, including coronary slow flow phenomenon (CSFP) and diastolic dysfunction (DD). This study aimed to better understand the short-term alterations and indicators of improved diastolic function in CSFP patients presenting with NSTEMI. Methods: This prospective research was conducted on 100 NSTE-ACS patients undergoing coronary angiography. Echocardiographic measures were employed to determine diastolic function, and the TIMI frame count approach was employed to determine the presence of CSFP. At the start of the study and after three months, clinical and angiographic data were gathered. Results: The mean age of the studied patients was 46 ±4 years. Significant improvements were noted in several diastolic function parameters at three months. At three months, there were significantly lower percentages of average E/Em > 14 (2% vs. 16%, P < 0.001), LAVI > 34 mL/m2 (46% vs. 76%, P < 0.001), lateral Em < 10 (61% vs. 76%, P < 0.001), and TR velocity (41% vs. 76%, P < 0.001) compared to baseline. Kaplan Meier analysis was done to calculate MACE-free survival. It showed that at 1.5 months, the MACE-free survival was 97.8% and 92.7% in those with improved and non-improved diastolic dysfunction, respectively. Conclusion: Our study shows the positive impact of diagnosing and managing CSFP in NSTE-ACS patients, as it may lead to improved diastolic function over a relatively short period.