I don't quite understand what you really mean by cutting the ribs underneath the heart. If it means from the spine, then the answer is 'No'; it cannot be done. However, bypass surgery can certainly be performed by cutting the ribs from the side, which is called lateral thoracotomy. However, when we do that, then certain areas of the heart are exposed well but other areas are not that well exposed. Therefore, if all three arteries are blocked, then one has to resort to cutting the sternum from the front. As for your premise that pain will be less, then let me tell you, the pain is the least in the front incision, called the sternal incision and is definitely more when a cut is made in the side.