Normal EF is 55 to 75%. An EF40% indicates the heart is not putting into circulation with each heartbeat a blood supply that may or may not meet the system demand for oxygen rich blood. If the demand for blood/oxygen such as when there is heavy and prolonged exertion, there may be no symptoms that would include shortness of breath and possibly chest pain, etc. Then it may be dangerous under those circumstances.
Since there was recent surgery, I don't believe an EF 40% is unexpected and may also depend on your husband's condition prior to bypass. May require more time to recover from the traumatic event of surgery, and more importantly is how your husband feels.
had bypass surgery in December 2007 not 08....sorry