cardiac surgery

my hasbend 62 y old he did by pass surgery 3 monthes ago and they told us that his EF 10-15 and they recomend the surgery and now after surgery he feel fine he did exersis 20 minutes every day and his BP 120/70 and his pulse80-85 no complain and after 3 monthes pass for the surgery the docter did echocardiography and he said his EF 37% and he recommend implantable defibrelator my hasbend dont want that my q to you if we wait other 3 monthes and follow the diet and exersic other more improvement can happend or no ? thank u for your response.