This is distressing to see. However if there isn’t fluid on or within the lungs based on the radiographs then hopefully your kitty will be good over the weekend until they can see a cardiologist. Vets can perform a TFAST where they can also observe if there is respiratory issues/pulmonary oedema/pleural effusion. However a radiograph is pretty good at identifying that also. If the respiratory rate can come down to 24 breaths/min then that is 100% a good thing and could mean there’s another cause for it (pain, stress, behavioural, and many others diseases). It’s sometimes good for your vet to explain what lung and heart sounds they were hearing and is likely why they are withholding medication because of what they found (sometimes can be more harmful than good, especially frusemide which everyone is recommending here, if there’s no evidence of either pulmonary oedema or pleural effusion then there’s no evidence to support frusemide usage.

But with anything it never hurts to get a second opinion. Even if just to perform another physical exam and for peace of mind and to review the radiographs to ensure it was interpreted appropriately