MY 16 Year Old Dog Has A #2 Heart Mummer

MY 16 year old dog has a #2 heart mummer had blood work done last monday her liver and kiney number were good. We have been having really hot weather the last few day our house has air but she seems to be coughing 5/6 times a day where as when the weather was colder she only cough 2/3 times should we be worried is it just the heat?