In light of the demonstrated presence of a mass which cytology has confirmed is a sarcoma, the weight loss is likely due to that disease (cancer cells use and waste a lot of energy). It is also possible that the
heart murmur is an incidental finding,
in other words has no real significance, especially as compared to the other problems. Further, many cats with undiagnosed inflammatory bowel disease (IBD) (the cat form of "irritable bowel" are chronic intermittent vomiters.