I agree coughing will be due to fluid building up in the lungs if the hearts weaker than a normal one...........the fruisamide (water tablets) helps with this, although toilet visits will be more frequent. Gentle exercise helps as it stops the fluid settling, my Rosie used to cough in the mornings after sleeping during the night.
The good news was she lived on medication until she was 14 years old and had a heart condition for a number of years prior but it didn't stop her having a fun filled life on medication, I can honestly say I have never met a happier dog than Rosie was.
Just enjoy each day for what it is......