The transtelephonic ECG (TTECG) has been shown to have a great value in the management of out-of-hospital chest pain emergencies since ST-segment elevation myocardial infarction (STEMI) is a life-threatening condition that demands prompt diagnosis and intervention. It has been shown that the TTECG-based consultation between paramedics and specialist improved the pre-hospital medical therapy (more frequent administration of sodium-heparin) and in- hospital mortality in ST-segment elevation myocardial infarction. It was hypothesized that the observed lower in-hospital mortality was mainly due to better coronary flow before primary percutaneous coronary intervention. In the present work we have directly proven that the more frequent administration of sodium-heparin in the TTECG group was associated with significantly less total coronary occlusions (p=0.0437) and intracoronary thrombus rate (p=0.0241), compared to controls. Moreover, the coronary flow before percutaneous coronary intervention was also significantly (p=0.0490) higher in the TTECG group as compared to controls. Our findings indicate that 1)recording and transmitting of TTECG and the TTECG-based consultation between paramedics and cardiologists during the first medical contact of STEMI patients is important for the optimal medical care and 2) prehospital administration of sodium-heparin reduces thrombus formation and occlusion. To conduct this study, we retrospectively evaluated all coronary angiograms in our patient cohort (775 patients) with special focus on coronary flow before and after primary PCI. We examined whether the use of prehospital TTECH in the diagnosis of STEMI and the more frequent administration of sodium heparin provided any benifit for coronary reperfusion. Our secondary objective was to investigate the difference of pre- and post- PCI TIMI grade and TIMI frame count between two groups which were the TTECG and the Control group in anticipation of better flow in the more frequently pre-heparinized TTECG group.