Heart transplant donors are overwhelmingly people who have died, either from brain death or, increasingly, from circulatory death, and whose hearts are recovered and transplanted into recipients with end-stage heart failure. The gap between available donor hearts and the number of patients who need them remains one of medicine’s most persistent problems, but the past decade has seen a quiet revolution in who counts as a suitable donor. Hearts from people with hepatitis C, hearts that have stopped beating, hearts that once would have been discarded for being too old or too small or from a donor with a complicated medical history are now being transplanted with outcomes that look remarkably similar to those from “ideal” donors. Understanding how donors are selected, matched, managed, and preserved is central to understanding why more people are surviving the transplant waiting list than ever before.
Brain-Dead Donors and Donation After Circulatory Death
For most of heart transplant history, the only usable donors were people declared brain dead while their hearts were still beating. A ventilator kept oxygen flowing, the heart continued to pump, and surgical teams could recover it in a functioning state. This category, called donation after brain death, remains the majority of heart transplants performed worldwide. But it leaves out a large group of potential donors: people who die after their heart stops but whose brain death criteria are never formally met.
Donation after circulatory death has changed the math. In this scenario, life support is withdrawn, the heart stops, and after a legally defined waiting period, the organ is recovered. The challenge is obvious: once the heart stops receiving oxygenated blood, damage begins immediately. For years, this made circulatory-death hearts unusable. That changed with the development of machines that can restart and sustain the heart outside the body. International data suggest that adding circulatory-death donors could increase the donor pool by roughly 30 to 48 percent, with comparable survival outcomes to traditional brain-dead donor transplants.1American College of Cardiology. Emerging Frontier in Heart Transplantation: Donation After Circulatory Death In a matched comparison of 79 circulatory-death and 79 brain-dead donor transplants, 90-day survival was 92 percent versus 96 percent, and one-year survival was comparable between groups.2PubMed. Outcome after heart transplantation from donation after circulatory-determined death donors A multicenter U.S. trial randomizing 180 patients further confirmed similar six- and twelve-month survival between the two donor types.
How Donors Are Matched to Recipients
Matching a donor heart to a recipient involves more than blood type, though that remains important. Two dimensions matter most: immunological compatibility and physical size.
On the immune side, transplant teams need to know whether the recipient’s immune system has preformed antibodies that would attack the donor organ. Traditionally, this required a physical crossmatch, mixing donor cells with recipient serum in a lab dish to watch for a reaction. That test is accurate but slow, and speed matters when a donor heart has limited time outside the body. Virtual crossmatching has largely replaced the physical test in many centers. Instead of waiting for live donor cells, teams use detailed typing of the donor’s tissue markers and compare them against the recipient’s known antibody profile.3PubMed Central. Out with the old, in with the new: Virtual versus physical crossmatching in the modern era Studies in sensitized patients (those with high levels of pre-existing antibodies, often from prior surgeries or blood transfusions) have shown similar rates of rejection at two years whether the virtual or physical crossmatch was used.4The Annals of Thoracic Surgery. Impact of Virtual Crossmatch in Sensitized Heart Transplant Recipients The practical benefit is that the virtual approach can be done before the organ is even offered, shaving hours off the process.
Size matching is the other critical variable, and it turns out that the traditional method of comparing donor and recipient body weight is not the best predictor of trouble. A metric called predicted heart mass, which estimates the actual mass of the donor heart based on age, sex, height, and weight, performs better. When a donor heart is severely undersized by predicted heart mass, recipients face about a 34 percent higher risk of death in the first year compared to those who receive an appropriately sized organ.5PubMed. Predicted heart mass is the optimal metric for size match in heart transplantation Undersizing by traditional body weight alone did not carry the same risk, which means some transplant centers using older matching criteria may be accepting hearts that look fine on paper but are functionally too small. When a heart is too small for the recipient’s circulatory demands, the risk of primary graft dysfunction, where the new heart fails to pump adequately in the early post-transplant period, roughly triples.6PubMed. Donor predicted heart mass as predictor of primary graft dysfunction
The Push to Use “Marginal” Donors
The chronic shortage of donor hearts has forced the field to reconsider what makes a heart acceptable. Extended-criteria donors, sometimes called marginal donors, are those who fall outside traditional ideal parameters: they may be older, have diabetes or high blood pressure, have a history of cardiac arrest, or have used drugs. The proportion of transplants using these donors has grown steadily, but many organs from this group are still declined out of caution.
Recent evidence suggests that caution may be excessive in many cases. With careful selection, appropriate size matching, and aggressive early management, outcomes from extended-criteria donor hearts are comparable to those from standard donors.7PubMed Central. To Take or Not to Take: The Dilemma With Marginal Donor Heart? One area where this has been tested rigorously is donor drug use. A large analysis of donors with either a history of drug use or positive toxicology at the time of death found no difference in post-transplant survival compared to drug-free donors.8Circulation: Heart Failure. Intoxicated Donors and Heart Transplant Outcomes: Long-Term Safety In the context of the opioid crisis, where drug-related deaths have increased the pool of young, otherwise healthy potential donors, this finding has real practical weight.
Pediatric transplant data paint a similar picture. When evaluating potential donor hearts for children, transplant teams receive data on seven categories of donor information: cause of death, whether the donor needed CPR, troponin levels, use of medications to support blood pressure, projected time the heart will be without blood flow, and electrical and imaging studies of the heart. A review of the literature found that as long as the donor heart looks normal on echocardiography, none of the other categories meaningfully predicted worse outcomes for the child who received it.9Pediatric Transplantation. Effects of donor cause of death, ischemia time, inotrope exposure, troponin values, cardiopulmonary resuscitation, electrocardiographic and echocardiographic data on recipient outcomes In other words, the echocardiogram is doing most of the heavy lifting in predicting whether a donor heart will work, and teams may be over-weighting other data points when deciding to decline an organ.
Hepatitis C Donors and the Antiviral Revolution
One of the most striking expansions of the donor pool involves hearts from donors infected with hepatitis C. Until recently, these organs were almost universally declined. The arrival of direct-acting antiviral drugs, which cure hepatitis C in nearly everyone who takes them, upended that calculation. Transplant programs began accepting hepatitis C-positive hearts and treating recipients with antivirals immediately after surgery.
The results have been striking. In one proof-of-concept trial, 20 recipients of hepatitis C-positive hearts received antiviral treatment starting right after transplant. Every single recipient cleared the virus, with a median time to undetectable levels of just three and a half days. Patient and graft survival were 100 percent at a median follow-up of about 11 months.10The Lancet Gastroenterology & Hepatology. Pre-emptive direct-acting antiviral therapy in patients receiving heart transplants from hepatitis C virus-infected donors A larger study confirmed that one-year survival for recipients who developed hepatitis C infection from donor hearts was about 90 percent, not significantly different from recipients of hepatitis C-negative hearts during the same period.11JAMA Cardiology. Expanding Heart Transplant in the Era of Direct-Acting Antiviral Therapy for Hepatitis C These findings effectively turned a previously disqualifying infection into a manageable, temporary condition, opening up a meaningful number of additional donor hearts each year.
How Donor Hearts Are Kept Alive Outside the Body
The traditional method of preserving a donor heart is simple: flush it with a cold solution and pack it on ice in a cooler. This static cold storage buys roughly four to six hours before the heart sustains too much damage to transplant, and shorter is always better. Every additional hour of cold ischemia raises the odds of the heart struggling when it is restarted in the recipient.
Ex vivo heart perfusion machines have changed this equation. These portable devices pump warm, oxygenated blood (or a blood-based solution) through the donor heart continuously during transport, keeping it in a near-physiological, beating state. The technology was originally developed to make circulatory-death hearts viable, since those hearts have already experienced a period without blood flow and cannot tolerate additional cold storage time as well. But the benefits extend beyond that niche. Ex vivo perfusion enables the use of donor hearts that would otherwise be excluded due to long transport distances or borderline donor characteristics, and outcomes so far have been comparable to standard cold storage.12PubMed Central. Heart transplant advances: Ex vivo organ-preservation systems The machines also allow transplant teams to assess heart function in real time during transport, something cold storage cannot offer. A heart that looks marginal in initial assessments can sometimes prove itself during perfusion, while one that performs poorly can be declined before it reaches the operating room.13Transplant International. Ex-Vivo Heart Perfusion Machines in DCD Heart Transplantation Model: The State of Art
Managing the Donor Before Procurement
Once a potential donor is identified and consent is obtained, intensive medical management of the donor’s body becomes critical. Brain death triggers a cascade of hormonal and hemodynamic instability: blood pressure can swing wildly, body temperature drops, and hormone levels crash. Left unmanaged, these changes damage the heart before it ever reaches a recipient.
Hormonal resuscitation therapy, which typically includes steroids, vasopressin, and thyroid hormone, has been standard practice for years. One study found that when this therapy was started early and maintained for at least 15 hours, 79 percent more hearts became transplantable compared to donors who did not receive it or received it for shorter durations.14PubMed. Relationship of hormonal resuscitation therapy and central venous pressure on increasing organs for transplant Careful fluid management, keeping central venous pressure low, further improved numbers across all organ types.
Interestingly, the thyroid hormone component of this protocol has come under closer scrutiny. A large randomized trial tested intravenous levothyroxine against saline placebo in hemodynamically unstable brain-dead donors and found no significant difference in the number of hearts transplanted, no improvement in the rate of weaning from blood pressure medications, and no change in heart function on imaging. The levothyroxine group actually had more episodes of severe high blood pressure and rapid heart rate.15PubMed Central. Intravenous Levothyroxine for Unstable Brain-Dead Heart Donors This is a case where a widely accepted practice turned out, under rigorous testing, to offer no clear benefit and some potential harm. It remains to be seen how quickly clinical protocols will adapt to this evidence.
Blood Type Barriers in Pediatric Transplants
Infants waiting for heart transplants have historically faced devastating mortality on the waiting list. Young children with blood type O, who can only receive compatible organs, have it worst because the donor pool is smallest relative to demand. A pioneering approach exploits a quirk of infant biology: babies younger than about 12 to 18 months have not yet developed the antibodies against mismatched blood group antigens that would cause older children and adults to immediately reject an incompatible organ.
The earliest published series of ABO-incompatible infant heart transplants showed 80 percent survival, with no cases of hyperacute rejection, and waiting list mortality at the program dropped from 58 percent to 7 percent simply because more donors became available.16PubMed. ABO-incompatible heart transplantation in infants This was not a subtle improvement. It was the difference between most babies dying while waiting and most babies getting a transplant.
The practice has since become routine. By 2017, about 72 percent of children under two listed for heart transplant were listed as eligible for ABO-incompatible donors, up from 49 percent in 2010. For blood type O patients, this shortened waiting time significantly.17PubMed. A current era analysis of ABO incompatible listing practice and impact on outcomes in young children requiring heart transplantation Long-term follow-up data from a multicenter study confirmed that ABO-incompatible transplants in young children produced survival, rejection rates, and rates of coronary artery disease in the graft that were all statistically similar to compatible transplants. An unexpected bonus emerged: children who received incompatible hearts actually had fewer serious bacterial infections, particularly from encapsulated bacteria, suggesting that the immunological changes required to tolerate a mismatched organ might confer some protective benefit.18The Lancet Child & Adolescent Health. Long-term outcomes after ABO-incompatible pediatric heart transplantation: a multicentre, prospective cohort study
How Allocation Policy Shapes Who Gets a Heart
In the United States, a major overhaul of the heart allocation system took effect in 2018. The old system had three tiers of urgency. The new one has six, designed to better distinguish among the sickest patients and prioritize those most likely to die without a transplant. The results have been measurable: waiting list mortality dropped (90-day mortality fell from about 6.3 to 5 percent, and one-year mortality from 13.3 to 11.7 percent), and the average time spent waiting was cut dramatically, from about 135 days to 55 days.19JAMA Cardiology. Evolving Trends in Adult Heart Transplant With the 2018 Heart Allocation Policy Change
The tradeoff is geography. Under the old system, donor hearts tended to stay relatively close to where they were procured, with an average distance of about 157 miles between donor and recipient hospitals. After the policy change, that average jumped to about 279 miles, and cold ischemia time grew correspondingly, from about three hours to nearly three and a half. The system essentially decided that getting hearts to sicker patients faster was worth the increased logistical complexity and slightly longer preservation times. So far, post-transplant survival has not suffered, but the shift has placed a premium on efficient procurement logistics and, increasingly, on portable perfusion machines that can handle longer transport windows.
The Experience of Donor Families
The donor side of heart transplantation involves a grieving family making one of the most consequential decisions of their lives under extreme time pressure. Research on donor families reveals that the emotional aftermath is more complex than the uplifting narratives often presented in media campaigns. Nearly half of donor families experience grief at high levels, and guilt emerges as a significant factor closely linked to other emotional difficulties.20PubMed Central. Impact of organ donation on grief symptoms in donor families Families who had a better understanding of brain death at the time of the decision tended to report lower grief levels afterward, suggesting that clearer medical communication during those critical hours can make a lasting difference in how families process the experience. Access to counseling and grief support after donation remains inconsistent across hospitals and organ procurement organizations.
Pig Hearts and the Xenotransplantation Frontier
If the donor shortage cannot be fully solved by expanding human donor criteria, the most radical alternative is to use hearts from other species. Xenotransplantation, specifically using genetically modified pig hearts, has moved from science fiction to early clinical reality. Pigs are the species of choice because their hearts are similar in size and anatomy to human hearts and because genetic engineering has made it possible to remove pig genes that trigger immediate human immune rejection and add human genes that help the organ coexist with the recipient’s immune system.
Two living patients have received genetically modified pig hearts under compassionate-use authorization. Both were people with end-stage heart failure who were not candidates for a traditional human transplant. They survived for 40 and 60 days respectively, with the transplanted pig hearts eventually failing in both cases.21Circulation. Cardiac Xenotransplantation: Current State and Future Directions The first of these patients, a 57-year-old man with advanced cardiomyopathy, received a heart from a pig with ten individual gene edits and was treated with an immunosuppressive regimen built around blocking a specific immune signaling pathway.22PubMed Central. Genetically Modified Porcine-to-Human Cardiac Xenotransplantation Separately, pig hearts were transplanted into two recently deceased human recipients (brain-dead individuals maintained on ventilators for research purposes) and monitored for 66 hours. Neither heart showed signs of hyperacute rejection or evidence that pig viruses had transmitted to the human recipients.23PubMed. Pig-to-human heart xenotransplantation in two recently deceased human recipients
The results are encouraging enough to sustain serious investment, but they also illustrate how far the technology has to go. Both living recipients ultimately died, and the immune barriers beyond the immediate rejection phase remain formidable. Xenotransplantation is not yet a solution to the donor shortage. It is an active, expensive experiment that may eventually become one.
Opt-In Versus Opt-Out Donation Systems
Countries differ in how they structure organ donation consent. In opt-in systems (like the United States), you must actively register as a donor. In opt-out systems (like Spain, France, and Austria), everyone is presumed to be a donor unless they specifically decline. The intuition is that opt-out systems should produce dramatically more donors, since inertia favors donation. The evidence is more complicated than that.
An international panel study found that deceased donor rates were higher in opt-out countries, roughly 14 per million population versus 10 per million in opt-in countries. But living donation went in the other direction, with more living donors in opt-in countries. When you look at total transplants (kidneys from both deceased and living donors combined), opt-out countries still came out ahead.24PubMed Central. An international comparison of deceased and living organ donation/transplant rates in opt-in and opt-out systems: a panel study A separate analysis, however, argued that the policy itself deserves less credit than it typically gets. When studied in isolation, switching from opt-in to opt-out confers no obvious advantage and can even harm donation efforts if it is not accompanied by broader infrastructure improvements like trained donation coordinators, ICU capacity, and public education campaigns.25PubMed Central. Assessing Global Organ Donation Policies: Opt-In vs Opt-Out Spain, often held up as the gold standard for organ donation, is an opt-out country, but experts widely attribute its success to its network of in-hospital transplant coordinators rather than to presumed consent alone. The policy debate, in short, is less about which box people check and more about whether the systems around that checkbox are designed to convert potential donors into actual ones.