Introduction. Patients presenting with tachycardia most often complain of palpitation and dizziness, but can also report episodes of chest pain due to increased myocardial oxygen demand. The aim of this case article was to emphasize the importance of differential diagnosis between different types of supraventricular (SVT) or ventricular tachycardia (VT) according to ECG findings, and highlight the treatment algorithm for wide QRS-complex tachycardia. Case Outline. We present a 34-years old female patient which was admitted to our hospital due to palpitations and chest pain that occurred at rest about two hours before hospital admission. Cardiac auscultation showed the presence of irregular heartbeats with tachycardia, whereas arterial blood pressure was 100/60 mmHg. Initial ECG recording demonstrated wide complex tachycardia (WCT) with irregular heart rate of approximately 180 beats per minute with right bundle branch block-like morphology of QRS complexes. After administration of intravenous amiodarone, patient was converted to sinus rhythm, with short PR interval (< 120 ms) and narrow QRS complexes (< 120 ms) with visible delta waves, indicating the presence of Wolff?Parkinson?White syndrome type A as the underlying cause of atrial fibrillation with right bundle branch block-like morphology of QRS complexes. Conclusion. The ability to differentiate between VT and SVT with a wide QRS complex due to aberrant intraventricular conduction or preexcitation is critical because the treatment of each is different, and inadequate therapy may potentially have lethal consequences.