Learn ECG: Free Interactive Electrocardiogram Reference | Opti ECG

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Explore the heart, make sense of the trace, and learn through interactive guides.

Conduction Leads Waves & intervals Axis Rhythms Veterinary Foundations

New to ECG? Start with the basics.Learn the paper, then build your first systematic read.

All guides

Every reference page, grouped by topic.

ECG Leads14

Limb Lead I
Limb Lead II
Limb Lead III
Augmented Lead aVR
Augmented Lead aVL
Augmented Lead aVF
Precordial Lead V1
Precordial Lead V2
Precordial Lead V3
Precordial Lead V4
Precordial Lead V5
Precordial Lead V6
Limb Leads Overview
Precordial Leads Overview

Conduction System8

Sinoatrial Node
Atrioventricular Node
Bundle of His
Right Bundle Branch
Left Bundle Branch
Left Anterior Fascicle
Left Posterior Fascicle
Purkinje Fibers

Cardiac Axis8

Normal Cardiac Axis
Left Axis Deviation
Right Axis Deviation
Extreme Axis Deviation
Left Ventricular Hypertrophy
Right Ventricular Hypertrophy
How to Determine Cardiac Axis
Cardiac Axis in Veterinary ECG

ECG Rhythms25

Normal Sinus Rhythm
Sinus Bradycardia
Sinus Tachycardia
Atrial Fibrillation
Atrial Flutter
Premature Atrial Complexes
Premature Ventricular Complexes
Supraventricular Tachycardia
Ventricular Tachycardia
Ventricular Fibrillation
Torsades de Pointes
First-Degree AV Block
Second-Degree AV Block Type I (Wenckebach)
Second-Degree AV Block Type II (Mobitz II)
Third-Degree AV Block
Right Bundle Branch Block
Left Bundle Branch Block
Wolff-Parkinson-White Syndrome
Junctional Rhythm
Wandering Atrial Pacemaker
Multifocal Atrial Tachycardia
Left Anterior Fascicular Block
Left Posterior Fascicular Block
Idioventricular Rhythm
Asystole

ECG Intervals & Waves6

PR Interval
QRS Complex
QT Interval
ST Segment
P Wave
T Wave

Veterinary ECG10

Canine ECG Overview
Canine Normal Sinus Rhythm
Canine Atrial Fibrillation
Common Canine Arrhythmias
Canine Cardiac Axis
Canine ECG Lead Placement
Feline ECG Overview
Species ECG Comparison
Veterinary ECG Interpretation Guide
Heart Rate Ranges by Species