ECG Cheat Sheet 2026

The 30 highest-yield ECG facts, distilled from real exam questions. Print it, save it as a PDF, or study it here — free, no sign-up.

1. Nitroglycerin relieves angina but its primary ECG effect during an acute ischemic episode would be: → Reducing or resolving ST segment depression or elevation as ischemia improves
2. The technician notices the ECG stylus is not returning to baseline between beats. The most likely cause is: → Stylus position or damping issue requiring machine adjustment
3. Which interval is measured from the beginning of the Q wave to the end of the S wave? → QRS duration
4. The standard ECG paper speed used in the United States is: → 25 mm/sec
5. When performing an ECG on a patient with a pacemaker, what should the technician note? → Document pacemaker presence and note pacemaker spikes on the tracing
6. Which precaution is essential when performing an ECG near an MRI suite? → Do not bring ferromagnetic ECG equipment into the MRI environment zone
7. Wandering baseline artifact on an ECG tracing is most often caused by: → Patient movement or respiration
8. A patient receiving IV adenosine for SVT would most likely show which transient ECG finding immediately after the dose? → Complete heart block or brief asystole
9. Patient confidentiality regarding an ECG recording is protected under: → HIPAA
10. V4 is positioned at the: → Fifth intercostal space, midclavicular line
11. V5 is placed at which line, level with V4 and V6? → Anterior axillary line
12. What voltage does each large square on ECG paper represent at standard calibration? → 1 mV
13. What does a prolonged QT interval increase the risk of? → Torsades de pointes
14. A wandering baseline artifact on an ECG is most often caused by: → Patient movement or loose electrodes
15. Sotalol (a Class III antiarrhythmic with beta-blocking properties) increases the risk of torsades de pointes primarily because it: → Prolongs the QT interval
16. A patient presents with chest pain and the ECG shows ST-segment elevation in leads II, III, and aVF. Which coronary artery is most likely involved? → Right coronary artery
17. Which finding on a rhythm strip indicates a normal sinus rhythm? → Upright P wave before every QRS at 60-100 bpm
18. Which of the following is a correct step in preparing skin for ECG electrode placement? → Wipe skin with alcohol and allow to dry
19. Which action is required if an ECG technician notices a life-threatening arrhythmia on the tracing? → Notify the responsible clinician immediately and do not leave the patient alone
20. How many small squares represent 0.04 seconds at standard ECG paper speed (25 mm/sec)? → 1 small square
21. Which federal law requires healthcare facilities to maintain a safe electrical environment for patients receiving ECGs? → National Electrical Code (NEC) / Joint Commission EC standards for medical facilities
22. If the right arm and left arm electrodes are accidentally reversed, Lead I will typically show: → An inverted (negative) P wave and QRS
23. A PR interval greater than 0.20 seconds with all P waves conducting to QRS indicates: → First-degree AV block
24. What color is the LA (left arm) electrode in the American (AHA) color code? → Black
25. A patient with Parkinson's disease is likely to produce which type of ECG artifact? → Somatic (muscle tremor) artifact
26. A supraventricular tachycardia (SVT) on the monitor typically appears as what? → A regular narrow-complex tachycardia at 150-250 bpm
27. The ST segment on the ECG represents: → The period between ventricular depolarization and repolarization (plateau phase)
28. The T wave on the ECG corresponds to what physiological event? → Ventricular repolarization
29. An ECG technician notices a patient's rhythm strip shows bradycardia and first-degree AV block. Which medication history is most consistent with these findings? → Metoprolol (beta-blocker)
30. T-wave inversion in leads V1–V4 in an adult is most concerning for: → Anterior ischemia or right heart strain