What Does an Electrocardiogram Show?

Many heart problems change the heart’s electrical activity in distinct ways. An electrocardiogram (EKG) can help detect a number of heart problems.

EKG recordings can help doctors diagnose a heart attack that’s happening now or has happened in the past. This is especially true if doctors can compare a current EKG recording to an older one.

An EKG also can show:

• Lack of blood flow to the heart muscle
• A heart that’s beating too fast, too slow, or with an irregular rhythm (arrhythmia)
• A heart that doesn’t pump forcefully enough (heart failure)
• Heart muscle that’s too thick or parts of the heart that are too big
• Birth defects in the heart (congenital heart defects)
• Problems with the heart valves (heart valve disease)
• Inflammation of the sac that surrounds the heart (pericarditis)

An EKG also can reveal whether the heartbeat starts at the top right part of the heart like it should. The test shows how long it takes for the electrical signals to travel through the heart. Delays in signal travel time may suggest heart block or long QT syndrome.