No you cannot.
This is a public board and posting information like this constitutes 'publication' and becomes prosecutable as a defamation action. Both you and I would be liable. You are free to go tell whoever you want but you CANNOT post such statements here. This is clearly stated in the getting Started section and I encourage everyone who has any question about what they may post to review this section.
As unfortunate as this is -- and I am so, so sorry you have had this diagnosis and discovered it in such a terrible, unsupportive way -- one person's experience, bad or good, may or may not represent typical care and there could be many reasons why information wasn't conveyed, including that it was misheard, someone was supposed to be in touch who wasn't, etc. In other words -- basic and unintended human error. While frustrating this is not necessarily neglectful in the eyes of the law, especially if the issue was crossed wires or if there are at this stage no additional meds that would be needed. Most murmurs are not treated until the dog goes into CHF (but at the same time -- I'd see a cardiologist at this point and would be rightly angry not to have understood a dog had a murmur of this grade).
I'd also inform the breeder as this is critical information for a breeding programme.
Vet care can vary widely so I do recommend finding a vet whose care satisfies what people want in terms of out of hours care (if provided -- many do not offer such a service), general demeanour, approach to care, etc.
I hope you can get better information on what to do at this point from a new vet and perhaps support from a cardiologist; hope a cardiologist might not think the murmur is at this level (only a cardio can really ensure an accurate reading). Vets are not generally good at estimating murmur grade.
I'm going to close this particular thread but please do open a separate discussion about the diagnosis and where to go from here and general advice, if you'd like.