An “unclassified” result on your Kardia device means the recording captured a readable heart rhythm, but the algorithm couldn’t sort it into one of its known categories. It’s not an error, and it doesn’t necessarily mean something is wrong. It simply means your heart rhythm fell outside the specific patterns the device is programmed to recognize.
What Kardia Can and Can’t Identify
Kardia’s algorithm is FDA-cleared to detect four specific things: normal sinus rhythm, atrial fibrillation, bradycardia (slow heart rate), and tachycardia (fast heart rate). That’s a short list. The human heart can produce dozens of different rhythm patterns, and if yours doesn’t match one of those four, the device labels it “unclassified” rather than guessing.
This is an important distinction. Unclassified doesn’t mean abnormal. It means the software reached the limits of what it’s designed to do. Premature beats (PVCs or PACs), certain arrhythmias, pacemaker rhythms, and even completely harmless variations can all trigger an unclassified result simply because they don’t fit the device’s narrow detection window.
Heart Rate Outside the Detection Range
One of the most common reasons for an unclassified result is straightforward: your heart rate was too high or too low for the normal-rhythm algorithm. Kardia flags a recording as unclassified when the heart rate falls below 40 bpm or above 140 bpm. If you just finished exercising, drank a lot of caffeine, or recorded while feeling anxious, a temporarily elevated heart rate alone could be the cause. Similarly, some people naturally run a resting heart rate in the low 40s, especially athletes, and this can trip the threshold.
Unclassified vs. Unreadable
These two results mean very different things, and it’s worth knowing the difference. An unclassified recording means the device got a clean signal but couldn’t categorize the rhythm. An unreadable recording means the signal itself was too poor for the algorithm to analyze at all. If you see “unreadable,” the issue is almost always technical: poor contact with the electrodes, too much movement during the recording, or electrical interference. You can usually fix it by re-recording. An unclassified result, on the other hand, is based on a successful recording. The tracing is usable and can be reviewed by a healthcare provider.
What Causes Signal Problems
Sometimes a recording lands on “unclassified” partly because subtle noise in the signal makes the rhythm harder for the algorithm to interpret, even if it doesn’t reach the level of “unreadable.” Common sources of signal interference include poor skin-to-electrode contact, muscle tension in your hands or arms, movement during the recording, and nearby electronic devices. Dry skin is a frequent culprit. Slightly moistening your fingertips with water before recording can improve conductivity. Cleaning the electrode surface on the device also helps.
For the best signal, sit still, rest your arms on a flat surface like a table, and relax your hands. Avoid pressing too hard on the electrodes, which can introduce muscle noise. Take a few calm breaths before you start.
What to Do With an Unclassified Result
A single unclassified result with no symptoms is rarely a cause for concern. Try recording again a few minutes later when your heart rate may have settled into the 40 to 140 bpm range. If the second recording comes back normal, the first one was likely just a momentary variation.
If you’re getting repeated unclassified results, that’s worth paying attention to. The recording itself contains useful data even though the app can’t categorize it. Kardia lets you save and share your tracings as PDFs. A nurse practitioner or cardiologist can look at the raw tracing and identify rhythms the device’s algorithm isn’t built to detect. In clinical programs that use Kardia for remote monitoring, review of unclassified tracings by a healthcare provider has been identified as critical for catching potentially significant arrhythmias that the device can’t categorize on its own.
If you notice symptoms alongside unclassified readings, such as dizziness, chest discomfort, shortness of breath, or a pounding or fluttering sensation, share those recordings with your doctor sooner rather than later. The combination of symptoms and an unclassifiable rhythm is exactly the kind of information that helps a provider decide whether further testing is needed.
Why the Algorithm Is Conservative
Kardia is designed as a screening tool, not a diagnostic one. Its algorithm intentionally errs on the side of caution. Rather than risk mislabeling a complex rhythm as “normal” and giving false reassurance, it defaults to “unclassified” when it isn’t confident. This is a feature, not a flaw. It means that when the device does say “normal,” that result carries more weight. The tradeoff is a higher rate of unclassified results, which can feel frustrating but reflects a deliberate choice to prioritize accuracy over certainty.