What Does an ECG Test Show? A Plain-English Guide

An ECG (electrocardiogram) records the electrical activity of your heart. It looks complicated, but it's really just a graph of when each part of your heart fires. Here's what the test actually reveals.

1. Your heart rate

How many times your heart beats per minute. Normal resting range is 60–100 bpm. Below 60 can be fine (athletes) or a sign of a conduction problem. Above 100 at rest is worth investigating.

2. Your heart rhythm

Is your heart beating in a steady pattern? An ECG flags irregular rhythms like atrial fibrillation, atrial flutter, premature beats, and heart block. Many of these are silent — you don't feel them — but they raise stroke and heart-failure risk over time.

3. The electrical pathway

The signal that makes your heart beat travels along a specific path. The ECG measures intervals (PR, QRS, QT) — how long each leg of the journey takes. Abnormal intervals can point to conduction issues, electrolyte problems, or drug effects.

4. Past or ongoing heart muscle damage

A previous heart attack leaves an electrical scar. Even a "silent" heart attack from years ago shows up as Q waves or ST/T changes. Active issues — like reduced blood flow to the heart muscle — show up as ST elevation or depression.

5. Chamber enlargement

If a chamber of your heart is working too hard for too long (often due to high blood pressure), it thickens. The ECG shows specific voltage patterns that hint at this.

What an ECG does NOT show

• Blocked coronary arteries — that needs an angiogram or CT
• Valve problems — that needs an echo
• Cholesterol — that's a blood test
• Exercise capacity — that's a TMT (treadmill test)

An ECG is a snapshot of electrical health. It's the cheapest, fastest first look — and for many conditions, it's the only test you need to flag the problem.