ST elevation appears as a visible upward shift of the flat line (the ST segment) that sits between the main spike of the heartbeat and the following rounded wave on an EKG tracing. Normally, this segment runs along the same flat baseline as the rest of the tracing. When it’s elevated, it looks like someone pushed that portion of the line upward, sometimes subtly, sometimes dramatically enough that the entire complex resembles a gravestone.
Understanding what ST elevation looks like matters because its shape, height, and location across the EKG’s 12 leads tell clinicians whether someone is having a heart attack, or whether something far less dangerous is going on. Here’s what to look for and how different patterns compare.
Where to Look on the Tracing
Every heartbeat on an EKG produces a repeating pattern: a small P wave, a tall QRS spike, and a rounded T wave. The ST segment is the short, normally flat stretch between the end of the QRS spike and the start of the T wave. The exact point where the QRS ends and the ST segment begins is called the J-point, sometimes described as the first inflection on the upstroke of the last downward dip of the QRS complex.
To judge whether the ST segment is truly elevated, you need a reference line. That reference is the flat stretch just before the P wave (the PR segment). Elevation is measured from the top edge of that baseline to the top edge of the ST segment at the J-point. Using the wrong baseline, such as the flat stretch between heartbeats, can produce inaccurate readings because electrical activity from the upper chambers of the heart can distort that area.
The Three Main Shapes of ST Elevation
Not all ST elevation looks the same. The shape of the upward shift carries important diagnostic clues, and three patterns dominate.
Concave (smiley face): The elevated ST segment dips slightly in the middle, creating a gentle upward curve that looks like the bottom of a bowl or a smiley face. This is the shape most often seen in benign conditions. It’s the classic appearance in early repolarization (a harmless normal variant common in younger people) and in pericarditis, the inflammation of the sac around the heart. However, concave elevation does not automatically rule out a heart attack. Research has confirmed cases of acute heart attacks presenting with concave ST elevation in the chest leads, which makes shape alone an unreliable way to distinguish a heart attack from other causes.
Convex (frowny face): Here, the elevated segment bulges upward in the middle, creating a dome or frowny-face shape. This pattern is traditionally associated with an acute heart attack and is considered more concerning than the concave form.
Straight (oblique): The ST segment rises in a straight, angled line from the J-point into the T wave without any obvious curve. Like the convex pattern, a straight ST elevation is considered more suggestive of a heart attack than a concave one.
The Tombstone Pattern
The most dramatic and dangerous-looking form of ST elevation is called “tombstoning.” In this pattern, the ST segment rises so high that it completely engulfs or overtakes the R wave (the tall upward spike of the QRS). The result is a broad, tall, rounded shape that visually resembles a tombstone or a rectangular monument. Specific features include a tiny or absent R wave, a convex ST segment that merges directly with the T wave, and a peak that sits higher than whatever R wave remains.
Tombstoning appears most often in anterior heart attacks (about 40% of cases with this pattern) but can also show up in inferior heart attacks (roughly 11%). It signals a large area of heart muscle at risk and is associated with more severe outcomes.
What Comes Before: Hyperacute T Waves
ST elevation doesn’t appear out of nowhere during a heart attack. The earliest visible change is often a shift in the T waves, which become what’s called “hyperacute.” These T waves look distinctly different from normal ones: they’re tall, broad-based, and symmetrical, sometimes described as looking like a large tent or a peaked mountain rather than the usual gentle, slightly lopsided bump. The base of these T waves may also sit lower than normal.
Hyperacute T waves are short-lived. They develop within minutes of a coronary artery closing off and quickly evolve into frank ST elevation. Recognizing them on a tracing can provide a critical early warning before the more obvious ST changes appear.
Reciprocal Depression: The Mirror Image
One of the most reliable signs that ST elevation represents a true heart attack rather than a benign mimic is the presence of reciprocal ST depression, essentially a downward shift of the ST segment in leads that look at the heart from the opposite direction.
In inferior heart attacks (where the bottom of the heart is affected), ST elevation appears in leads II, III, and aVF. Reciprocal depression shows up in the leads looking at the opposite wall, particularly lead aVL, where the depression roughly equals the elevation seen in lead III. In one study, every patient with an inferior heart attack showed reciprocal depression in either aVL or aVR. Lead aVF depression tends to be about half as deep as lead III’s depression, and lead II often shows no significant change at all.
In anterior heart attacks (affecting the front wall), the pattern reverses. ST elevation appears across the chest leads, and mild depression shows up in the inferior limb leads, though it’s typically smaller, often 1 mm or less.
How Pericarditis Looks Different
Pericarditis produces ST elevation that can easily be confused with a heart attack at first glance, but the overall pattern on a 12-lead EKG is distinct. Instead of elevation confined to a specific region of the heart, pericarditis causes diffuse elevation spread across most limb leads (I, II, aVL, aVF) and chest leads V2 through V6. It also produces a subtle but telling clue: the PR segment (the flat line just before the QRS) dips below the baseline in those same leads.
The shape of the elevation in pericarditis is typically concave. Most importantly, there is no reciprocal ST depression except in leads aVR and V1, which normally point in the opposite direction from everything else. The absence of reciprocal changes in the standard leads is one of the strongest visual clues separating pericarditis from a heart attack. About 60% of pericarditis cases follow this typical pattern of diffuse elevation followed by normalization and then T-wave inversions over days to weeks.
Benign Early Repolarization
In younger, otherwise healthy people, it’s common to see mild ST elevation of 1 to 4 mm in the chest leads, especially V2 through V5, with the most elevation in V3. This pattern, sometimes called “early repolarization” or “high take-off,” features concave ST elevation with a distinctive notch or small hump at the J-point. That notch, sometimes called a fishhook or J-wave, is most visible in leads V5 and V6 and is one of the best visual markers distinguishing this normal variant from something dangerous.
There’s typically no reciprocal depression, no hyperacute T waves, and no clinical symptoms. The tracing looks stable over time rather than evolving through the stages seen in a heart attack.
When ST Elevation Hides
Some heart attacks produce patterns that don’t fit the classic ST elevation picture. Two situations are especially tricky.
Left Bundle Branch Block
When the heart’s electrical wiring is already disrupted by a left bundle branch block, the entire QRS and ST segment look abnormal at baseline, making it difficult to spot new changes from a heart attack. A set of criteria called the Barcelona algorithm helps clinicians identify heart attacks in this setting by looking for ST changes that move in the same direction as the main QRS deflection (at least 1 mm of elevation) or ST changes that move in the opposite direction from the QRS when the QRS itself is small (0.6 mV or less).
The de Winter Pattern
Sometimes a major artery supplying the front of the heart is completely blocked, yet the EKG shows ST depression rather than elevation. The de Winter pattern features 1 to 3 mm of downsloping ST depression at the J-point across chest leads V1 through V6, paired with tall, peaked, symmetric T waves. It looks almost like the inverse of what you’d expect, yet it signals the same emergency. This pattern is considered a “STEMI equivalent,” meaning it requires the same urgent treatment as classic ST elevation even though the ST segments technically point downward rather than upward.