After open heart surgery rashes around the wound? why?

Variable: There can be any number of reasons. But, presuming it is not an infection, the most common cause is tape reaction from the bandage. Alternatively, some get a reaction from hair removal with clipper.

Rash : Most likely fro the tape or dressing. Redness may be just normal healing or inception. It needs to be serially followed. The incision needs to be washed with soap and water.

Many possibilities: There are many things that could cause a skin rash. Several types of inflammatory conditions of the skin, allergic reactions, sun exposure, insect bites, and sometimes bacterial, viral or fungal infections can cause rashes on the skin. Have it evaluated by a professional and get the appropriate treatment.