That’s a very good question, and to be honest I find it much easier to think about the benefits of them – many people die while waiting for a transplant organ to become free, and artificial organs can work around that. However, as with everything, there are drawbacks.
One problem may be battery life – I read about one type of artificial heart whose battery lasted 30 minutes, but could be charged through the skin by a battery pack in a vest. Those packs only lasted 4 hours though, so not ideal all in all. It’s also the case that surgery to remove a natural heart and insert an artificial one is an enormous undertaking – the trauma can mean the patients (many of whom are quite ill anyway) struggle to recover.
More common than full artificial hearts, it seems, are devices which help your heart to pump more powerfully. These are also large and bulky, but less traumatic to insert – more like working with your heart than replacing it. And for the future scientists are hoping to make 3d printed silicone artificial hearts – smaller, lighter and more like the real thing 🙂