I've been there, twice.
Izzy, at 7, was diagnosed, at routine vaccination time, as having a middle sized murmur and this was a big shock, because of his breeding. he had no symptoms for a year, then developed a cough, which just like you, I first assumed was kennel cough, as he had been in contact with it. By the time he got a cough, his murmur was off the scale, yet drugs gave him two more good years.
A few weeks after Izzy's diagnosis, I was told that Monty, too had a very mild murmur, barely noticeable (he would have been 9). Last year it was up to lower middle and now at !2 and a half is slightly more , but he only developld a cough a few months ago. He sometimes paces at night, but that is something he has always done, now and then. ( He wants to be on the bed, but is more comfortable on the floor.)
Monty only usually has a single hack, early in the morning, but this could be brought on by the fact that he licks himself. The vet said he is borderline drugswise and there is debate about thier effects at this early stage of heart failure, so he gave me the choice. As there was nothing to lose, I went for drugs and , now, he's on Fortekor and Frusemide.
At three month checkup, the good news was that the drugs have helped as his heart rate is lower, his pulse good, lip colour and lips reaction also good.
The main heart drugs in UK are Fortekor and Vetmedin ( Izzy ended up taking both) with Frusemide, a generic, which comes under various names like Frusecare to help with water retention.
Barbara, Monty, Joly and Teddy.