It appears not everyone is happy about the first of its kind heart transplant from a genetically modified pig to human.

The high risk experimental transplant carried out on 57-year-old David Bennett at the University of Maryland Medical Center after doctors say he was too ill to qualify for a human heart.

Considering the huge risks for the patient as even a well-matched human donor organ can be rejected after they are transplanted – and with animal organs the danger is likely to be higher.

While the breakthrough surgery is being hailed by many as a way to shorten transplant waiting list, some are questioning the ethical justification of the procedure.

Apart from patient safety, animal rights and religious concerns are some of the troubling issues     around the science.

Bennett’s treatment has reignited the debate over the use of pigs for human transplants, which many animal rights groups oppose.

One of them, People for the Ethical Treatment of Animals (PETA) has condemned Bennett’s pig heart transplant as “unethical, dangerous, and a tremendous waste of resources”.

“Animals aren’t tool-sheds to be raided but complex, intelligent beings,” PETA said.

Campaigners say it is wrong to modify the genes of animals to make them more like humans. Scientists altered 10 genes in the pig whose heart was used for Mr Bennett’s transplant so it would not be rejected by his body.