Bruno Reichart: Ethics play an important role here. We've been eating pigs for a long time, so it's socially acceptable to kill them. Also, pigs produce many offspring in a very short time — every four months — and they are fully grown and sexually mature after six months.
A pig's heart is also very similar in structure to a human heart. The valves from pigs' hearts have been used as a replacement in humans for 40 years.
This is part of what the authorities demand: The organ should not be implanted into a pig or a dog but a primate that's very close to us biologically, so conclusions can be drawn as to whether the intervention could also be successful in humans.
You have to adapt the pig's heart to that of a human in order to prevent the recipient's body rejecting the transplant. Which is why the pig hearts are genetically modified before they are transplanted.
Just a few months ago critics argued there were too many to such transplants — saying that pig hearts lacked the pumping capacity of a human heart, and that porcine endogenous retroviruses (PERV) in the pig genome could put human patients at risk.
I have to say, the people who wrote this unfortunately had little idea what they were talking about and should have done a bit more reading. A pig's heart pumps excellently in the body of a baboon or human.
There has never been an infection from viruses in pig tissue. There are three types of porcine endogenous retroviruses: A, B and C. C is very aggressive so we have to use animals that are C-negative, or don't have C viruses due to breeding or genetic modification.
This happens in the egg cell. You have to remove a gene, which is relatively easy nowadays with CRISPR-Cas9 scissors. You can use it to destroy the C-PERV copies in the pig genome and make them harmless.
What would be the advantage of a pig's heart over current transplant options?
This would have the advantage of addressing the enormous shortage donors. And that's our goal — that a pig's heart isn't just a bridging measure, but a final transplant.
Is this the moment of breakthrough?
There will have to be some more breakthroughs, I'm afraid. Now we need money, because these trials cost a lot. We have to find an investor, and that's very difficult in Europe. For me, it's currently a full-time job.
What would it mean if pig hearts became a real alternative? Would production farms suddenly appear everywhere?
At the moment, a few pigs and their offspring would be sufficient for the pilot study. And later, you would certainly need 1,000 pigs — this is still a long way off. The pigs already exist, but for organ transplants you would need very high hygiene standards. We don't have such capabilities anywhere yet.
How can you be sure this will work?
You always have throw yourself into the unknown. But it's very unlikely this will not work.
Bruno Reichart is professor emeritus at the University Hospital in Munich and one of the most distinguished heart transplant experts in Germany. In 1983, he successfully carried out the first heart-lung transplant in Germany. Today, he works on xenotransplantation — the transfer of cells, up to entire organs, between different species.
The interview was conducted by Anne Höhn.
More love for your heart
An international study found many of us believe only older people are at risk of heart attacks - and as a result, that only older people have to be careful. But the German Heart Foundation says that's not true. The earlier you start looking after your heart - through an active lifestyle and healthy diet - the better. After all, you've only got one heart!
Nifty little pump
The heart is a marvel of technology. The fist-sized, hollow muscle contracts about 70 times per minute, pumping up to 10,000 liters of blood through the body. And it does that your whole life. If necessary, the heart can pump about five times that much blood - for instance, when we are jogging.
Real muscle work
The heart may be "just" a muscle - but it's a very special one. Like the muscles in your legs and arms, it can contract as fast and with as much power. But the heart has incredible stamina, and never gets tired. What's more, all heart muscle cells are linked, so they contract in unison.
If a heart beats slower than it should, a patient can be fitted with a pacemaker. First implanted in 1958, the device sends electrical impulses to the heart muscle. These days, pacemakers can function for from five to 12 years - on average, about eight.
To operate on a heart, surgeons have to stop it temporarily. This halts the circulation of blood - which would technically be fatal. But in the 1950s, scientists were able to solve this problem by developing the heart-lung machine. That machine takes over the function of the heart and lungs, enriching the blood with oxygen and pumping it through the body.
The heart via the groin
Modern medicine allows doctors to examine and perform surgery on the heart without cutting open the patient's ribcage. Instead, an intracardiac catheter - more or less a thin plastic tube - is inserted through veins and arteries in the groin, the elbow or the wrist. This tube is then pushed into the heart, requiring only local anesthesia.
Foldable heart valve
If a heart valve is not working or worn out, you need a new one. Doctors might use a biological replacement from pigs, and mechanical heart valves made from metal are also an alternative. Modern artificial heart valves are foldable (pictured above) and can be inserted in endoscopic surgery via a catheter. This way, no open-heart operation is needed.
Putting heart into it
The first heart transplantation took place in 1967 - quite a sensation, back then. Nowadays, this operation is no longer a rarity. Every year, surgeons around the world transplant several thousand donor hearts from people who have died. The patients who receive a donor heart, however, have to take medication for the rest of their lives to prevent their own body from rejecting the foreign organ.
A pump inside
Donor hearts are rare, and there are waiting lists for recipients. If a heart is not working properly anymore, an artificial heart may support it. In that case, the sick heart stays in the body, and is supported by an implanted pump. This pump is powered by an external energy supply.
One research dream is to create an artifical heart that can replace the sick patient's heart completely. It would be inserted into the body, not require any external connection and would beat for many years without failure. Not an easy task - although some prototypes already exist.