ECGECG Interpretation

Develop interpretation skills in ECG Basics, analyze 12-lead tracings in ECG Library, and advance proficiency in ECG Reviews.

R Wave


The R wave is the first upward deflection after the P wave and part of the QRS complex. The R wave morphology itself is not of great clinical importance but can vary at times.

S Wave


The S wave is the first downward deflection of the QRS complex that occurs after the R wave. However, a S wave may not be present in all ECG leads in a given patient.

QuizQuizzes and Cases

Test your cardiology knowledge with Quizzes and Cases on a variety of topics including Atrial Fibrillation, Coronary Artery Disease, ECG Interpretation and more. Choose Study Mode to review the answers as you go; or choose Test Mode to challenge your fastest time. You can even build your own custom quizzes!

Quiz of the Week

Atrial Fibrillation

Question 1 of 28

Which of the following oral anticoagulants directly inhibits thrombin?

CardiologyCardiology Review

Broaden your understanding with hundreds of Topic Reviews, Facts and Pearls on important topics in cardiology, and Mnemonics to learn about cardiology.

Atrial Fibrillation Topic Review


Atrial fibrillation is the most common chronic arrhythmia, characterized by erratic atrial electrical activity with atrial rates of 400 to 600 beats per minute.

Mitral Regurgitation Topic Review


The normal mitral valve permits unrestricted antegrade diastolic flow from the left atrium to the left ventricle (LV) and effectively seals off the atrium from the ventricle during LV systole, allowing atrial filling from the pulmonary veins at low pressures.