My cat started to drink a lot I was convinced he maybe was diabetic and took him to the vet, they quickly noticed that his Thyroid was enlarged and he was given daily medication. I was warned of the time that quite often heart problems arise with thyroid issues and that proved to be the case A couple of years later although of course he might well have developed heart issues anyway. I was aware of the need to get the matter dealt with promptly as I also have thyroid issues. He was well medicated until the end and survived with his thyroid problems for five years before passing away at the age of 17. Bizarrely I had always kept an eye on his water consumption and was particular about the level of water in his dish when it was replenished, that is how I picked up the problem in the first place. It is a very common condition and cats but one which is easily treatable, but can be hugely detrimental if left. I speak only from my own experience I'm not qualified to comment in a professional capacity. Hope this helps.