ECG vs Echocardiogram:
What Is the Difference?

In my cardiology practice at Victoria Medical, one of the most common questions I hear from patients is: "My GP mentioned I might need a heart test — is that an ECG or an echocardiogram, and what is the difference?" It is an entirely reasonable question. Both tests investigate the heart, both are painless, and both can be arranged quickly without a GP referral. But they measure fundamentally different things, and understanding that distinction helps you arrive at your appointment with clarity rather than anxiety.

An ECG — electrocardiogram — records the electrical signals that make your heart beat. An echocardiogram uses ultrasound to create a moving image of your heart's structure and mechanical function. Think of the ECG as listening to the orchestra's timing, and the echocardiogram as watching the musicians themselves. Both perspectives are valuable; neither replaces the other.

What an ECG Measures

Every heartbeat begins with an electrical impulse generated in the sinoatrial node — the heart's natural pacemaker — which then travels through a precisely coordinated pathway to trigger each chamber to contract in sequence. An ECG captures this electrical journey in real time, producing the familiar waveform trace that cardiologists read to assess rhythm, rate, and conduction.

A standard 12-lead ECG, which is what we perform at Victoria Medical, places ten electrodes on the skin of the chest, arms, and legs to record the heart's electrical activity from twelve different angles simultaneously. This multi-angle view is clinically important: a deep neural network trained on over 2.3 million ECG records demonstrated F1 scores above 80% and specificity exceeding 99% for detecting six major ECG abnormalities, outperforming cardiology residents in pattern recognition^[1].

The conditions a 12-lead ECG can identify include atrial fibrillation and other arrhythmias, heart block and conduction delays (bundle branch blocks), evidence of a previous or ongoing heart attack (ST-segment changes), left or right ventricular hypertrophy, and the effects of certain medications and electrolyte imbalances. What an ECG cannot do is show you the physical structure of the heart — the size of the chambers, the condition of the valves, or how powerfully the muscle is pumping.

What an Echocardiogram Shows

An echocardiogram is an ultrasound scan of the heart. High-frequency sound waves are directed at the chest wall and bounce back to create real-time moving images of the heart's chambers, valves, and surrounding structures. Unlike an ECG, which takes seconds to record, a standard transthoracic echocardiogram typically takes 30 to 45 minutes and provides a comprehensive structural and functional assessment.

The clinical value of echocardiography is well established. Data from echocardiography provide a cornerstone in the management of heart failure, with all major imaging techniques able to derive ejection fraction — the percentage of blood pumped out of the left ventricle with each beat^[3]. A normal ejection fraction is 55–70%; values below 40% indicate significant impairment and guide treatment decisions.

For valve disease, echocardiography has demonstrated sensitivity of 72–97% across multiple studies, making it the gold standard for assessing aortic stenosis, mitral regurgitation, and other valvular conditions^[5]. Tissue Doppler echocardiography — a more advanced technique we use at Victoria Medical — can detect diastolic dysfunction with a specificity of 100% at the appropriate cut-off value, making it particularly useful for diagnosing heart failure with preserved ejection fraction (HFpEF)^[4].

Critically, an echocardiogram cannot tell you about the heart's electrical activity. A patient can have a perfectly normal echocardiogram — healthy valves, good ejection fraction, normal chamber sizes — and still have atrial fibrillation or a dangerous conduction abnormality that only an ECG would detect.

Key Differences at a Glance

The table below summarises the principal differences between the two tests. Understanding these distinctions helps explain why your cardiologist may recommend one, the other, or both during a single consultation.

When You Need an ECG

An ECG is typically the first cardiac test requested when a patient presents with symptoms that suggest an electrical or rhythm problem. In my practice, I recommend a 12-lead ECG as the starting point for patients experiencing palpitations — the sensation of a racing, fluttering, or irregular heartbeat. Palpitations are one of the most common cardiac complaints I see, and an ECG can immediately identify whether they are caused by atrial fibrillation, supraventricular tachycardia, ectopic beats, or a benign sinus arrhythmia.

An ECG is also the primary investigation for chest pain, particularly when there is concern about acute coronary syndrome or a previous myocardial infarction. ST-segment elevation on an ECG is the hallmark of a heart attack in progress; Q waves indicate prior infarction. Importantly, the ACC/AHA guidelines recommend echocardiography as a complement to ECG when clinical history is unavailable or unreliable during a chest pain episode^[6].

Other situations where an ECG is the appropriate first-line test include: unexplained syncope (fainting), pre-operative cardiac screening, monitoring of patients on medications that affect heart rhythm (such as certain antidepressants or antiarrhythmics), and annual cardiac review for patients with known hypertension or diabetes.

When You Need an Echocardiogram

An echocardiogram is the investigation of choice when the clinical question is structural rather than electrical. If a patient presents with breathlessness that has progressively worsened over weeks or months, or with ankle swelling that suggests fluid retention, my first concern is heart failure — and an echocardiogram is the definitive test to confirm or exclude it. Echocardiography provides a cornerstone assessment in heart failure management, enabling measurement of ejection fraction, identification of diastolic dysfunction, and assessment of cardiac output^[3].

For patients with a heart murmur — an abnormal sound heard through a stethoscope — an echocardiogram is essential to characterise the underlying valve abnormality. Echocardiography has demonstrated sensitivity of 72–97% for detecting valve disease across multiple studies, making it far superior to clinical examination alone^[5]. An ECG in the same patient may be entirely normal, or may show only non-specific changes that do not guide management.

I also recommend an echocardiogram for patients with a strong family history of cardiomyopathy or sudden cardiac death, for those with hypertension who need assessment of left ventricular hypertrophy and diastolic function, and for athletes undergoing cardiac screening. The echocardiogram answers questions that no other non-invasive test can address as comprehensively.

When You Need Both Tests

In clinical practice, the ECG and echocardiogram are frequently complementary rather than mutually exclusive. The ACC/AHA guidelines have long recognised that a complete cardiac assessment for chest pain, heart failure, or complex arrhythmia often requires both an electrical and a structural perspective^[6]. Furthermore, research has shown that an abnormal ECG has lower sensitivity for diagnosing heart failure with preserved ejection fraction (HFpEF) — echocardiography was present in 71% of HFpEF patients, confirming that ECG alone is insufficient for this diagnosis^[2].

At Victoria Medical, when a patient presents for a comprehensive cardiac assessment — particularly if they have multiple symptoms or risk factors — I typically perform both tests in the same appointment. The ECG takes five minutes; the echocardiogram follows immediately. Together, they provide a complete picture of both the electrical and structural health of the heart, enabling a definitive diagnosis and a clear management plan without the need for multiple separate visits.

What to Expect at Victoria Medical

Both tests are available at our clinic at 170 Vauxhall Bridge Road, two minutes from Victoria Station. No GP referral is required, and same-day appointments are typically available. Here is what the process looks like.

Frequently Asked Questions