Your heart doesn't just produce electrical signals it produces magnetic fields too. And those magnetic fields carry information that electricity misses.
In our previous post, we talked about a surprising gap in modern medicine: despite cardiovascular disease being the world's leading cause of death, there is no routine screening test for the heart in your annual check-up. The ECG, when included, misses too much.
So what's the alternative? The answer lies in something most people don't realise their heart produces: a magnetic field.
Every time your heart beats, a coordinated wave of electrical current sweeps through the heart muscle. This is what the ECG measures the electrical voltages that reach the skin surface. But there's a fundamental law of physics (known as the Biot–Savart law) that says whenever an electrical current flows, it also produces a magnetic field around it.
Your heart's electrical activity therefore generates two signals simultaneously: an electrical one and a
magnetic one. The ECG measures the first.
Magnetocardiography (MCG) measures the second.
The heart's magnetic field is extraordinarily faint roughly 50 picotesla at the chest surface. To put that in perspective, the Earth's magnetic field is about a billion times stronger. Detecting the heart's magnetic signal is like trying to hear a whisper during a rock concert. It requires extremely sensitive instruments.
But here's the crucial point: the magnetic signal carries information that the electrical signal does not.
To understand why MCG can see things that ECG cannot, you need to understand one key difference in the physics.
When your heart's electrical signal travels outward to reach the ECG electrodes on your skin, it passes through multiple tissue layers — heart muscle, pericardium, lung, ribcage, subcutaneous fat, skin. Each of these tissues conducts electricity differently. Fat is a poor conductor. Bone is even worse. Lung tissue, filled with air, is different again. The result is that by the time the electrical signal reaches the skin, it has been distorted, attenuated, and smeared by the body's own tissues.
The magnetic field, on the other hand, passes through all of these tissues essentially undisturbed. This is because biological tissues are not magnetic their magnetic permeability is virtually identical to that of a vacuum (to within one part in a million). Skin, fat, bone, muscle, lung — magnetically, they are all transparent.
Like listening to someone speak through a thick, uneven wall. You hear the rhythm, but the words are muffled. Different wall sections distort the sound differently.
Like watching someone speak through a clean glass window. The signal arrives undistorted. You see every detail of the movement clearly.
The physics in brief
The ECG signal depends on the electrical conductivity of every tissue it passes through and conductivity varies by a factor of 20× between muscle and bone. The MCG signal depends on the magnetic permeability, which is the same (μ₀) in all body tissues to within 0.0001%. This is why MCG provides a more faithful spatial picture of cardiac electrical activity. It's not an engineering trick it's a fundamental law of physics.
This physical advantage translates directly into clinical advantages. Because the magnetic signal preserves the spatial structure of cardiac currents, MCG can localise the source of abnormal activity to within about 5 mm compared to 15–20 mm for ECG. It is also sensitive to current flows that run parallel to the chest wall, which are particularly important in early ischaemia but are nearly invisible to standard ECG leads.
Perhaps the most important clinical advantage of MCG is this: it can detect signs of coronary artery disease at rest, without requiring the patient to exercise or undergo stress testing.
When a coronary artery is partially blocked, the heart muscle downstream doesn't get enough oxygen. This creates subtle changes in the electrical behaviour of the affected heart cells — particularly during the "repolarisation" phase when the cells reset between beats. These changes produce altered magnetic field patterns that MCG can detect.
Multiple clinical studies have demonstrated this capability, with reported sensitivity and specificity for detecting coronary artery disease ranging from 80% to 93%.
Published clinical studies have demonstrated MCG sensitivity of 80–93% for detecting coronary artery disease — compared to approximately 50% for resting ECG — and MCG achieves this without any stress induction, contrast agents, or radiation.Sources: Tolstrup et al., American Heart Journal, 2006; Hailer et al., PACE, 2005; Shin et al., Annals of Noninvasive Electrocardiology, 2019
Unlike angiography which involves threading a catheter into your arteries an MCG test is completely non-contact. The patient experience would be:
No needles, no preparation, no fasting. You simply lie on a bed.
30 secondsA sensor array is positioned above your chest. It doesn't touch you.
1 minuteLie still and breathe normally while the system records your heart's magnetic field.
5 minutesSoftware analyses the magnetic signal and flags any patterns associated with ischaemia or coronary artery disease.
MinutesNo radiation. No contrast dye. No catheter. No exercise. Just five minutes lying on a bed.
An important point: MCG is not meant to replace coronary angiography. Angiography remains the gold standard for definitive anatomical diagnosis — for determining exactly where a blockage is and how severe it is. What MCG provides is the screening step that currently doesn't exist.
Think of it like a mammogram and a biopsy. A mammogram screens the general population and identifies who might have a problem. Only those with positive results go on to a biopsy for definitive diagnosis. MCG would function the same way for heart disease: screen broadly, identify abnormalities, and refer only those patients who need it for invasive angiography.
| Feature | MCG (Screening) | Angiography (Confirmation) |
|---|---|---|
| When used | Routine check-up, asymptomatic | After positive screening or symptoms |
| Invasiveness | Non-contact | Arterial catheter |
| Radiation | None | 5–15 mSv |
| Contrast agent | None | 50–150 mL iodinated |
| Duration | ~5 minutes | 30–60 min + recovery |
| Cost | ₹8,000 (target) | ₹50,000—₹3,00,000 |
| Repeatability | Unlimited | Limited by cumulative risk |
Currently, 30–40% of all diagnostic coronary angiograms come back "normal" — meaning the patient went through an invasive, expensive procedure only to find there was no significant disease. A reliable screening test like MCG could dramatically reduce this number, sparing patients from unnecessary procedures while ensuring those who do have disease are caught early.
If the physics is sound and the clinical evidence is strong, why isn't MCG in every hospital? The answer lies in the technology that has traditionally been needed to detect those incredibly faint magnetic fields. Until recently, the only sensors sensitive enough were superconducting quantum devices that required liquid helium cooling and million-dollar magnetically shielded rooms.
That's changing — fast. In our next post, we'll explain how a new generation of room-temperature quantum sensors is making MCG practical, portable, and affordable for the first time.
The heart produces a magnetic field that carries information the ECG misses. Measuring it could catch heart disease before the first symptom — and the test takes just five minutes.
Looking for clinical collaborators, hospital partners, and investors who share our vision.