Murmurs in young animals are often congenital but the fact that this murmur was not heard previously may indicate that this is a developing condition. While somewhat subjective, an enlargement of the heart would warrant an investigation of the murmur.
In our hospital, we often use a mobile Veterinary Radiologist/Ultrasound Specialist to evaluate heart conditions. Using Doppler ultrasound can help to determine the source of the murmur and pressure gradients across the murmur as well as heart muscle thickness and contractility. This information can help us determine the significance (or non-significance) of the murmur, treatment if any that may be indicated, and the possible long-term ramifications of the murmur, and whether a Veterinary Cardiologist should be consulted.
In our hospital, this procedure costs about what it would cost to neuter your pet. This information would be essential in determining the safety of anesthesia in this patient and the long-term prognosis and I would highly recommend this be done prior to any elective anesthesia and surgical procedure.