Heart Disease in Female 10 yr old

Hi, My lovely girl has been diagnosed with Heart Disease. She will be 10 on Jan 22nd. The vet gave her water tablets and some heart tablets but these just made her so unwell and she started having seizures and also became very distressed by having to wee and drink constantly. The vet also said she had to diet (she is 51kg) and short walks only.
I did some research and a side effect of the tablets is seizures!!! She never had them before and I am pretty sure that the Heart disease has been there a while and she has coped with it. So, I have taken her off the tablets and she is so much better! The diagnosis came after she kept stumbling on our walks and I thought she had hurt her leg, the xrays showed no signs of arthritis or injury, but a massively enlarged heart. She has no cough either.
My question is to other Bullmastiff owners- has this happened to any of your babies? If so, did treatment help or make it worse, did you still walk them?