That's rather a broad question but the simple answer is that some illnesses (e.g. amyloid) can affect multiple organs including the heart and the lungs. It is also possible there are two separate things going on in the lungs and the heart. I suspect the reason they want the biopsy is that they are not sure what is going on in the heart and want a piece of tissue to help make the diagnosis. Once the disease is known then prognosis can be determined.
I did some reading about restrictive cardiomyopathy and restrictive pericarditis. This indicated that it is very hard to distinguish between these two disease processes, and it may take surgery to definitively diagnose it. Do doctors biopsy myocardium/pericardium tissue during catherization(R or L)?
Or do they now do exploratory surgery similar to Laproscopy to distinguish between these disease processes instead of open heart surgery?
Thanks,
Ginny