Generally, patients need to avoid salt if they have congestive heart failure or difficult-to-control hypertension. Often, congestive heart failure is from a heart muscle that is weaker than normal. Too much salt intake leads to fluid retention and either edema (swelling in the legs) or shortness of breath, if the fluid accumulates in the lungs.
Your husband has cholesterol build-up in his coronary arteries, which necessitated needing the bypass operation. In theory, the best diet to prevent further atherosclerosis in the arteries and bypass grafts would be one high in fiber, low in sugar, low in simple carbs (starches that are quickly broken down into sugar in the stomach like white bread, white potatoes, and white rice), with protein and "good" fats (mono unsaturated fats like olive oil, avocado, nuts, and nut oils). A good diet, along with exercise and cholesterol-lowering medicines, is the best way to prevent heart attacks and strokes.
After major surgery, and particularly with heart problems, it is often difficult to regain adequate weight and muscle. It is important for him to exercise regularly, to the level he is able, as well as get in enough calories and protein. Since further cholesterol build-up is a slow and long-term problem, being off the ideal diet so he can get enough calories and protein from foods that he likes and is willing to eat, would be reasonable for a spell.
I think one generally feels better and more energetic with a healthy diet. I think you should be able to plan a high-calorie, high-protein diet, full of fiber, high-quality protein, and "good" fats. Talk to your doctor or nutritionist. And I hope your husband continues to rebound from his difficult year.