Echocardiogram vs ECG: electrical tracing or heart ultrasound?

The heart works as both an electrical system and a pump. An ECG tests the wiring: electrodes on the chest, arms and legs pick up the tiny voltages produced as the heart beats. An echocardiogram tests the plumbing and muscle: a probe on the chest sends sound waves that bounce back to create moving pictures of the heart.

Because of this, one test cannot substitute for the other. A normal ECG does not show whether a valve is leaking, and a normal echo does not rule out a rhythm problem that is not occurring during the scan.

A resting ECG is quick, cheap and informative. It can show atrial fibrillation, heart block, extra beats, signs of reduced blood supply, a past heart attack and patterns suggesting an inherited condition. It is usually the first heart test in primary care and in the emergency department.

Its limitation is that it only records the period you are connected. If your palpitations come once a week, a ten-second tracing may be normal. A mild structural problem or a leaking valve can also leave the ECG unchanged.

An echo measures how well the left ventricle squeezes, whether valves open and close properly, whether the heart chambers are enlarged, and whether there is fluid around the heart. It is the main test for suspected heart failure after a blood test or ECG, and for investigating a murmur.

It does not show the electrical rhythm in any detail, and image quality can be limited by body shape or lung disease. If the pictures are poor, contrast injection or alternative imaging such as cardiac MRI may be used.

In chest pain, ECG comes first, often with blood tests, because it can show an acute problem within minutes. In breathlessness or suspected heart failure, NICE guidance (NG106) points towards blood testing with natriuretic peptides and an echocardiogram where indicated. In palpitations, a longer rhythm recording matters more than an echo unless symptoms or the ECG suggest structural disease.

Where atrial fibrillation is found, NICE guidance (NG196) covers stroke prevention and rhythm management, and an echocardiogram is often used to look for underlying structural disease.

• Fluttering, racing or irregular beats: an ECG, and if normal but symptoms persist, ambulatory ECG monitoring.

• Breathlessness, swollen legs, reduced stamina: an ECG and blood tests first, then an echo if heart failure is plausible.

• A murmur heard by the doctor: echo to look at the valves.

• Chest pain on exertion: an ECG is a starting point, but further tests such as CT angiography or stress testing usually follow.

• Routine health check with no symptoms: neither test is generally recommended for everyone without a reason.

A normal ECG does not mean the heart is healthy; it means the tracing at that moment was normal. Likewise, an echo showing normal pumping does not exclude a coronary artery narrowing or an intermittent rhythm problem.

People also sometimes expect an echo to detect blocked arteries. It does not show the coronary arteries directly, though it can show the effects of reduced blood supply on heart muscle movement.