How can you clinically differentiate respiratory failure from heart failure?

Heart failure: Will be diagnosed as congestive heart failure. Pt's get sob and cxr and labs will show the usual findings of heart failure of fluid in the lungs. It can lead to respiratory failure. Resp failure need not be due to the heart and can just be failure of oxygenation, or ventilation if co2 rises, due to things like asthma, copd, and other lung causes, sepsis without overt heart failure, pe, etc.

Can be difficult: ... Because the two are connected. You should see a doctor. History and physical exam, as well as imaging studies like chest xray, or, if indicated, ct or echo, can be helpful.