I'm Henry's mom. Thank you for your comments and suggestions. I am not as concerned. Henry has shown no change in energy over the last few years I've had him. He was adopted from a shelter about 4 years ago and he didn't have a heart murmur then. I will get a second opinion. I really don't want to put him through any extra stress. He tends to be uptight for a cat. Thanks, Sandie for posting the original question.