Thanks for the comments. Had some good news today, there is no evidence of malignant cells in the samples sent for testing, so with the lung x-rays clear and no sign of spread to the lymph nodes I am hopeful that the melanoma has been contained. I am over the moon with this result so if anyone has a knitting pattern for a mini schnauzer ear let me have it so I can knit her a prosthetic earflap!
I have decided not to do anything about the enlarged heart, this is the first chest x-ray she has ever had so who is to say how long it has been enlarged. She has no clinical signs of heart disease - no cough, no murmur, no exercise intolerance (she normally has a combination of free running and road walking - total of between 2 and 5 miles a day plus a good size garden to run about in) so, given how much she has been through lately I think I will leave well alone and just monitor her.