After a heart attack, the affected area of the heart changes dramatically in appearance, shifting from its normal deep reddish-brown color to a pale, mottled patch within the first 24 hours. Over the following weeks and months, that damaged zone transforms further, cycling through distinct visual stages as dead muscle is gradually replaced by scar tissue. What the heart looks like depends entirely on how much time has passed since the attack.
The First 24 Hours
A healthy heart is a uniform reddish-brown, with firm, muscular walls that contract in a coordinated rhythm. In the first few hours after a heart attack, the affected area looks surprisingly normal to the naked eye. The damage is happening at the cellular level, where muscle fibers start to buckle and warp from oxygen starvation. About 94% of heart attacks less than 24 hours old show these “wavy fibers” under a microscope, making it one of the earliest detectable signs of injury.
By 18 to 24 hours, the damage becomes visible on the heart’s surface. The area of dead muscle turns noticeably pale compared to the surrounding healthy tissue. Fluid seeps between cells, causing the region to swell slightly. In nearly all cases during this first week, the tissue shows widespread cell death and swelling, and about 77% of early infarcts also show some degree of bleeding within the damaged zone.
Days 2 Through 14
During the first two weeks, the dead region becomes increasingly distinct from the surrounding muscle. The tissue softens as immune cells flood the area to break down and clear away dead cells. Acute inflammation dominates the first week, with the body treating the dead muscle essentially like a wound. By the second week, that acute response shifts to a chronic one, and the damaged area can appear yellowish and fragile. This softening phase is actually the most structurally dangerous period. The weakened wall is at its highest risk of complications because the dead tissue is being actively dissolved but hasn’t yet been replaced with anything strong.
Bleeding within the damaged zone peaks during days 8 to 14, present in roughly 90% of cases. At the same time, new tiny blood vessels begin growing into the area at full speed. This new blood vessel growth is present in 100% of infarcts by the second week and remains a dominant feature for the next several weeks, supplying the raw materials the body needs to rebuild.
Weeks 3 Through 6
Starting around the second week, the body begins laying down collagen, the same tough protein found in tendons and skin scars. Through weeks three to six, connective tissue gradually replaces what was once living muscle. The damaged area transitions from a soft, fragile zone into something firmer and paler, taking on the whitish, fibrous appearance of scar tissue.
This process is slower and messier than most people expect. At four to five weeks, about 20% of infarcts still contain some areas of dead tissue that haven’t been fully cleared. In roughly a third of cases examined between three and five weeks, healing still isn’t complete. The entire process from initial injury to a fully formed scar typically takes five to six weeks at minimum, with collagen deposition continuing for about three months after the heart attack.
The Permanent Scar
Once healing is complete, the area where muscle died is replaced by a dense, white, fibrous scar. This scar is clearly visible on the heart’s surface, a pale patch that contrasts sharply with the surrounding dark muscle. During open-heart surgery, surgeons can immediately identify old infarct zones by this color difference and by the thinned, stiff quality of the wall in that region.
Unlike the rest of the heart, scar tissue cannot contract. It sits passively while the surrounding muscle works around it. This is why the location and size of the scar matter so much for long-term heart function.
How the Heart’s Shape Changes
A heart attack doesn’t just leave a scar. It can reshape the entire organ. This process, called ventricular remodeling, begins within hours and continues for months.
In the early phase, the damaged wall thins and stretches outward because dead muscle can’t resist the pressure of blood filling the chamber. This “infarct expansion” increases the overall size of the left ventricle and raises stress on the remaining walls. Over the following weeks and months, the heart responds to that extra stress by thickening its surviving muscle. Individual heart muscle cells can increase their volume by up to 70% to compensate.
The overall effect is that a heart with a large scar often loses its normal elliptical shape and becomes more spherical, or globe-like. The scarred segment stays thin and stiff while the opposite wall thickens. Imaging studies show that by about 11 days to 3 months after the attack, the scarred basal segment is visibly thinned and no longer moves, while the opposite wall contracts more vigorously to pick up the slack. A heart that has undergone significant remodeling looks noticeably enlarged and rounder than a healthy one.
What Imaging Reveals
Most people will never see their heart directly, but cardiac MRI can show the damage in vivid detail. The most common technique uses a contrast dye that washes quickly out of healthy muscle but lingers in scarred or dead tissue. On the scan, damaged areas light up bright white against the darker healthy muscle, allowing doctors to pinpoint exactly where the infarct is, how deep it extends through the wall, and how much total muscle was lost.
The depth of that bright signal through the heart wall is critical. If the damage only extends partway through, some of the muscle in that area may still be alive and capable of recovery. If the bright signal goes all the way through the wall, that segment is fully scarred and won’t regain function. Doctors use color-coded maps ranging from green (viable tissue) through yellow and orange to dark red (fully scarred) to visualize this gradient across the entire heart in a single image.
Echocardiograms, the more common ultrasound-based test, show the consequences rather than the scar itself. Segments of wall that don’t move or bulge outward during contraction mark where the damage occurred. Combined with the overall chamber size and pumping strength, these images paint a functional picture of how the heart attack reshaped the organ’s performance.