If you recently had a serious scare, such as a heart attack, I would want it out in the open so as not to block the flow of sexual energy. What I mean is... If you have something significant on your mind and you are trying to suppress it, sexually, that usually doesn't work. You'll be in your head instead of in your body.
The other reason I would want to know is if something goes wrong and you pass out or grab your chest. My response to call 911 is going to be quicker knowing you recently had a heart attack.
In my opinion, medical conditions don't take away from the fantasy of an experience. I would also expect my partner to "regulate" the strenuousness of our time together. If we need to slow down, please say so.