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. 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
5. Which precaution is essential when performing an ECG near an MRI suite? → Do not bring ferromagnetic ECG equipment into the MRI environment zone
6. Wandering baseline artifact on an ECG tracing is most often caused by: → Patient movement or respiration
7. 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
8. V5 is placed at which line, level with V4 and V6? → Anterior axillary line
9. What voltage does each large square on ECG paper represent at standard calibration? → 1 mV
10. A wandering baseline artifact on an ECG is most often caused by: → Patient movement or loose electrodes
11. Sotalol (a Class III antiarrhythmic with beta-blocking properties) increases the risk of torsades de pointes primarily because it: → Prolongs the QT interval
12. 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
13. Which finding on a rhythm strip indicates a normal sinus rhythm? → Upright P wave before every QRS at 60-100 bpm
14. Which of the following is a correct step in preparing skin for ECG electrode placement? → Wipe skin with alcohol and allow to dry
15. 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
16. How many small squares represent 0.04 seconds at standard ECG paper speed (25 mm/sec)? → 1 small square
17. 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
18. A PR interval greater than 0.20 seconds with all P waves conducting to QRS indicates: → First-degree AV block
19. What color is the LA (left arm) electrode in the American (AHA) color code? → Black
20. A patient with Parkinson's disease is likely to produce which type of ECG artifact? → Somatic (muscle tremor) artifact
21. The ST segment on the ECG represents: → The period between ventricular depolarization and repolarization (plateau phase)
22. 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)
23. T-wave inversion in leads V1–V4 in an adult is most concerning for: → Anterior ischemia or right heart strain
24. Peaked, narrow, symmetrical T-waves in multiple leads are a classic ECG sign of: → Hyperkalemia (early sign)
25. A patient taking quinidine (Class IA) develops a QTc of 560 ms. What is the most serious arrhythmia risk associated with this finding? → Torsades de pointes
26. Which lead configuration would produce a completely flat line (asystole appearance) if a limb lead becomes disconnected? → The affected lead traces flat while others remain
27. Which component of the ECG machine converts analog electrical signals to digital data? → Analog-to-digital converter (ADC)
28. Which artifact pattern can mimic ventricular fibrillation on an ECG? → High-frequency muscle tremor artifact
29. An ECG technician documents a QTc of 480 ms in a patient newly started on haloperidol (antipsychotic). What is the most appropriate action? → Document the finding and alert the supervising clinician for evaluation
30. What is the standard paper speed used for ECG recordings in the United States? → 25 mm/sec