BACKGROUND: Patients with ST-segment elevation myocardial infarction (STEMI) and heavy thrombus burden are at increased risk of distal embolisation and impaired reperfusion during primary percutaneous coronary intervention (PPCI). Conventional manual aspiration thrombectomy with a 30 mL syringe has shown limited benefit in large randomised trials. Increasing syringe volume to 50 mL may enhance suction efficiency and clot retrieval, offering a simple and cost-effective strategy to optimise reperfusion. METHODS: In this prospective cohort study, 88 consecutive STEMI patients with angiographic thrombus burden grade 4-5 undergoing PPCI were included. Group I (n = 44) underwent thrombectomy with a 30 mL syringe, while Group II (n = 44) underwent thrombectomy with a 50 mL syringe using an Export Advance catheter. Primary endpoints were post-procedural thrombolysis in myocardial infarction (TIMI) 3 flow and myocardial blush grade (MBG). Secondary endpoints included ST-segment resolution, echocardiography recovery (wall motion score index [WMSI] and left ventricular ejection fraction [LVEF]), and 30-day adverse cardiovascular events. RESULTS: Baseline clinical and laboratory characteristics were comparable between groups. The 50 mL syringe group achieved higher rates of complete reperfusion (TIMI 3 flow: 77% vs. 59%, p = 0.04; MBG 3: 59% vs. 45%, p = 0.05). The primary composite endpoint of TIMI 3 flow plus MBG 3 was significantly greater in Group II (59% vs. 41%, p = 0.04). ST-segment resolution (68 % 15% vs. 55 ± 12%, p = 0.01), immediate post-PCI WMSI (1.7 ± 0.4 vs. 2.1 ± 0.5, p = 0.002), one-month WMSI (1.5 ± 0.3 vs. 1.8 ± 0.4, p = 0.001), and LVEF (54 ± 5% vs. 49 ± 6%, p = 0.002) were all superior in the 50 mL group. At 30 days, cardiovascular events were numerically lower with the 50 mL syringe (2.3% vs. 4.1%, p = 0.17), with no increase in procedural complications. CONCLUSION: In STEMI patients with high thrombus burden undergoing PPCI, manual thrombectomy with a 50 mL syringe improved reperfusion, myocardial recovery, and procedural outcomes compared with the conventional 30 mL syringe, without added risk. This low-cost, accessible modification may represent a practical alternative to mechanical aspiration systems, warranting validation in larger randomised trials.