What is her resting respiratory rate? Depending upon this answer, it will determine if meds are needed. Since you notice a change, meds may likely be needed, but let's put a number to it.
When she lies down to sleep or nap and she's not excited or ideally she's actually sleeping, how many breaths does she take a minute?
Here's the information from the veterinary information network of specialists:
Why monitor SRR?
Owner participation in assessing and recording of Sleeping Respiratory Rate is:
Probably the most sensitive indicator of developing pulmonary edema or pleural effusion in dogs and cats.
A very useful home-monitoring technique for owners to perform.
Used once a diagnosis of CHF has been made (and is now controlled), or where substantial heart disease exists and is likely to result in CHF at some future stage.
In addition to being a great home monitoring aid, involving the owner in this process helps overcome the "need to do something" that many owners and veterinarians exhibit when dealing with heart disease.
How is it done?
Have the owner record the sleeping respiratory rate and character on their pet (number of breaths/min). The recording should be done when the animal is comfortably resting or asleep, in a thermo-neutral environment (ie, not too cold, not too hot). This should be repeated daily for 2-3 days (to get a baseline variation), and then once or twice weekly.
If the SRR changes substantially between measurements, the owner should then measure daily to confirm the change, or to document a trend. If a trend is documented, the owner should contact the veterinarian for further evaluation.
What is the normal SRR?
Normal SRR in dogs and cats is 30 breaths/min in patients with underlying heart disease is strongly suggestive of developing CHF. 25-30 is a bit of a grey area. However, primary respiratory disease with concurrent subclinical heart disease needs to be ruled out.
What else should owners look for?
Cats often have very subtle changes in demeanor or respiration prior to fulminant CHF.
Changes in appetite or activity or loss of weight in cats with known heart disease are often warning signs that CHF is imminent.
Coughing is a variable finding in CHF in dogs, and is not a feature of CHF in cats.
What do I do if SRR is high?
If SRR is elevated, thoracic radiographs and physical examination should be performed. If there is no clear evidence of CHF, a short diuretic trial can be employed (lasix @ 2mg/kg BID for 3-4 days). A reduction in the RRR to baseline with therapy further supports mild CHF.
Presence of sinus arrhythmia or sinus bradycardia is inconsistent with a diagnosis of CHF - nearly all animals with CHF will have sinus tachycardia.
First, I apologize because I am answering by mobile phone. Murmurs are not uncommon and it is difficult to say how it will affect your little girl. Since this is a new murmur, to stay proactive, there is a few options.
There is a test offered by Idexx laboratories called a canine proBNP blood test. This test is run to determine the likelihood of heart failure. Depending on the results, further diagnostics may be warranted.
Instead of running this test, chest radiographs (xrays) could identify enlargements of the heart and/or problems in the lungs attributed to heart disease. This could be attributed to the breathing changes.
Ultimately, an echocardiogram (ultrasound) of the heart could be important to determine the cause of the heart murmur.
I hope this has helped.
Thanks for the responses. I actually got the blood test done Saturday - her organs are functioning normally. I did notice her breathing was faster lately and she's been a little more lethargic than usual so I took her back Monday and had the vet do an X-ray. She has secondary tumors in her lungs so the heart issue is not the main problem anymore.