A LIMA graft is a bypass conduit made from the left internal mammary artery, a blood vessel in your chest that surgeons reroute to supply blood to your heart. It is the gold standard in coronary artery bypass surgery, with patency rates of 85% to 95% at 10 years. When someone needs bypass surgery for a blocked coronary artery, the LIMA graft is almost always the first choice.
Where the Artery Comes From
The left internal mammary artery (LIMA) branches off the subclavian artery, which sits just below your collarbone. From there, it runs down the inside of your chest wall, about two to three centimeters on either side of the breastbone. Its normal job is supplying blood to the front of your chest, the sternum, and the breast tissue. At around the sixth or seventh rib, it splits into two smaller branches that continue toward the abdomen and diaphragm.
What makes this artery special for heart surgery is its inner lining. The LIMA naturally produces chemicals that keep the vessel relaxed and resist plaque buildup, the same process that clogs coronary arteries in the first place. This biological advantage is why surgeons prefer it over other options.
How the LIMA Gets Connected to Your Heart
During coronary artery bypass grafting (CABG), a surgeon detaches the lower end of the LIMA from the chest wall while leaving the upper end connected to its original blood supply. The freed end is then sewn directly onto the blocked coronary artery, downstream from the blockage. Blood flows from the subclavian artery, through the LIMA, and into the heart muscle, effectively bypassing the clog.
The most common setup is a LIMA-to-LAD graft, meaning the artery is connected to the left anterior descending artery. The LAD is the most important coronary artery, supplying blood to a large portion of the heart’s left ventricle. This particular pairing has decades of evidence behind it and is the single most beneficial connection a surgeon can make during bypass surgery.
The surgery can be performed through a traditional open approach with a full sternotomy (splitting the breastbone) or through smaller incisions using robotic assistance. In the robotic approach, the surgeon harvests the LIMA using a camera and robotic arms through small ports in the chest, then performs the connection through a mini incision between the ribs. The stitching itself is done with extremely fine suture, typically at a scale of 7-0 (thinner than a human hair).
Why It Outperforms Vein Grafts
The other common bypass conduit is the saphenous vein, taken from the leg. Vein grafts work, but they deteriorate much faster. At 10 years, only about 25% of saphenous vein grafts remain fully open, compared to 90% or higher for mammary artery grafts. Vein grafts are prone to early failure, which can cause recurrent chest pain, reduced quality of life, and the need for repeat procedures.
The difference comes down to biology. The LIMA’s inner lining actively produces nitric oxide and prostacyclin, compounds that keep the vessel wall smooth, flexible, and resistant to cholesterol buildup. Vein grafts lose this protective effect over time. Their walls thicken, smooth muscle cells proliferate, and atherosclerosis accelerates, essentially recreating the same disease the surgery was meant to fix.
This is why current guidelines from the American College of Cardiology and American Heart Association treat the LIMA-to-LAD connection as a cornerstone of bypass surgery. When patients who previously had CABG need repeat procedures, surgeons weigh decisions partly based on whether a patent LIMA-to-LAD graft is already in place.
Using Both Mammary Arteries
You have two internal mammary arteries, one on each side. Using both (called bilateral internal mammary artery grafting, or BIMA) provides a survival advantage over using the left one alone. A meta-analysis of over 79,000 patients found that BIMA reduced long-term mortality by about 22% compared to single LIMA grafting.
Despite the better outcomes, most surgeons still default to using only the left. The main concern is infection. Harvesting both arteries reduces blood flow to the breastbone, which can lead to deep sternal wound infection in 0.3% to 14% of cases depending on technique and patient risk factors. This is a serious complication. The operation is also technically more demanding and takes longer.
Newer harvesting methods have narrowed this gap. Skeletonized harvesting, where the surgeon carefully isolates just the artery itself rather than taking it with a surrounding strip of tissue, preserves significantly more blood flow to the sternum. Randomized trials show that skeletonization causes much less damage to the small blood vessels that feed the breastbone. For diabetic patients, who face the highest infection risk, skeletonized bilateral grafting brings wound complication rates down to levels comparable to single LIMA grafting.
Skeletonized vs. Pedicled Harvesting
When surgeons take the LIMA off the chest wall, they have two main approaches. Pedicled harvesting removes the artery along with a cuff of surrounding fat, muscle, and veins. It is faster and technically simpler, but it can reduce blood flow behind the sternum by up to 50%. Skeletonized harvesting strips the artery free from its surrounding tissue, preserving the small collateral blood vessels that feed the breastbone.
The tradeoff matters most for healing. With pedicled harvesting, nearly all the small branching vessels that nourish the sternum are destroyed. Skeletonized harvesting with a harmonic scalpel (an ultrasonic cutting tool) may preserve more than half of those collateral branches. The result is better tissue oxygen levels behind the breastbone and a lower risk of wound complications. For patients receiving bilateral grafts or those with diabetes, skeletonization is increasingly considered the preferred technique.
Risks of LIMA Harvesting
The LIMA graft itself carries low risk, but the harvesting process is not entirely without complications. One recognized issue is injury to the phrenic nerve, which controls the diaphragm. This is more of a concern when harvesting the right internal mammary artery at its highest point, where the nerve runs nearby. In a study of 783 patients who had right mammary artery harvesting, phrenic nerve injury occurred in about 4% of cases, causing the diaphragm on that side to sit higher than normal and potentially affecting breathing. The good news: about two thirds of those patients recovered nerve function on their own without intervention.
A late closure rate of about 10% has been observed at 10 to 15 years even with LIMA grafts, though this is far lower than what occurs with vein grafts. The severity of the original coronary blockage also plays a role. When the LIMA is grafted to an artery with only mild narrowing, competitive flow from the native vessel can reduce graft performance over time.
Recovery After LIMA Graft Surgery
Recovery depends on the surgical approach. Traditional open bypass through a sternotomy typically involves 4 to 6 days in the hospital, with sternal precautions (avoiding heavy lifting, pushing, or pulling) for 6 to 8 weeks while the breastbone heals. Minimally invasive or robotic approaches that avoid splitting the sternum generally allow faster recovery, since the bone remains intact.
Regardless of approach, the LIMA graft itself begins working immediately. Blood flows through the new connection as soon as the surgery is complete. Over the following weeks and months, the graft matures and the connection site heals. Most patients return to normal daily activities within 6 to 12 weeks, with gradual increases in physical activity guided by cardiac rehabilitation.