Introduction/Objective: A diagnosis of STEMI can be made for patients with persistent chest discomfort or other symptoms of ischemia and an ST-segment elevation in at least two adjoining ECG leads. The differential diagnosis of ST-segment elevation consists of 4 major conditions: myocardial infarction, pericarditis, early repolarization syndrome, secondary changes and other diagnoses, such as pulmonary embolism (PE). The dilemma is whether an ST-elevation always requires the PPCI protocol to be activated? The objective of this article is to acquaint medical doctors with other similar clinical presentations and the importance of making the right decision that directly affects the course of treatment and the outcome for the patient. Case report: An 84-year-old woman called the EMS hotline complaining of chest pain and breathing difficulty. She was found in aprone position on a flat surface, pale and covered in sweat, but without chest pain at the ti. She had had hip replacement surgery and was discharged from the hospital two days earlier. She was currently receiving 0.4ml of Fraxiparine daily. Her blood pressure was 90/60mmHg, heart rate 115 per minute, breathing frequency 20 breaths per minute, blood oxygen saturation 70%. Upon auscultation, her heart sounds were softer, breathing was normal with no wheezing or crackles. ECG: ST-segment elevation in leads II, III and avF and reciprocal ST-segment depression in leads I, avL and V2-V6 and an S1Q3T3 pattern. Conclusion: There are many articles describing cases where the PPCI protocol had been activated for patients with similar ECG findings and who had been subjected to emergency coronary angiography. Since the coronary angiography findings had been normal and they were transferred for further diagnostics. Coronary angiography per se will not harm these patients, but delaying adequate treatment for pulmonary embolism could have a lethal effect. This is why it is very important to record serial ECG tracings. Rapid regression of ECG findings and Q-wave regression favorises pulmonary embolism.