Help, cat with possible UTI

My boyfriend just got out of the shower and went to pull some clothes out to put on and noticed that one of our cats had peed on his boxers. I've been reading other posts which have mentioned that peeing out of the litter box and on soft articles such as clothes is the #1 sign of a UTI. My cat isn't spayed due to having a severe heart murmur so I'm wondering if this is related or if simple antibiotics will cure the problem. I've been posting quite a bit about her in the last few days so it's probably good that I found this site in time. Is it time I just risked it and have her spayed although she will most likely die or will antibiotics work? Thanks for any help ahead of time...

Edit: Is a UTI correlated with not being spayed? I also forgot to mention that she got really mad at me earlier for petting her back end/belly area. Way more so than usual. Would she be in external pain or only internally?

Being in heat can often cause inappropriate urination. However, the cause could be a different behavioral issue or an infection. A visit to the vet is in order (along with a consultation with a cardiologist).

I wondered if being in heat could cause it but she's had previous cycles before and has never peed outside of the box. Plus the fact that it was in clothes (soft) worries me too. I'm planning on getting to the vets as soon as they call me back (called earlier today to make an appointment to listen to her heart again) Not sure if I'll be able to collect a urine sample but I'll give it a shot, yay...

Getting a urine sample isn't as hard as it sounds. They will give you this stuff called Nosorb. It's tiny plastic pellets. It won't absorb urine, just gives them someplace to scratch. Then you have to clean out the litterbox and put in the Nosorb. Put the kitty and the box in a room with a hard floor. Most people use the bathroom. Take up any rugs and plug the drain in the sink and tub. Lock the kitty in until she pees. Then you can suck up the urine in a syringe and put it in the cup the Nosorb came in. Be sure to refidgerate it if you're not taking it to the vet's right away.

Hope this helps.

Thanks for the comments. I took her in the other day and she doesn't have an infection, which is great but at the same time this means that it's behavioral, which isn't so great lol

AH ha! I have found the culprit. It looks like it was Otis doing the peeing not Mama, now I've got to figure the rest out. Can male cats get UTI?