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There are several issues involved –
Coughing triggered by eating suggests disorder of food pipe or stomach...
Coughing on walking or flat bed suggests left heart failure...
Swollen legs point to right heart failure
If they were not present before operation, this is abnormal and needs aggressive investigation
You have not stated his personal habits, co-morbidities, even age ...which could influence the diagnosis and outcome...
The treating doctor alone can suggest based on his examination, investigation and assessment of the situation.
Wishing speedy recovery