Thanks for your query.
It seems that you have gotten hit on the breastbone that lies in the middle-front part of the rib-cage. Heart is lying underneath this bone. So in an injury
of this bone, an injury to the heart or its membranes can be suspected. Another possibility is that you have injured the bone and/or the adjacent ribs. Thus it is imperative to do a detailed physical examination and investigations on you. The investigations can include X-rays of the chest, ECG of the heart, Imaging of the heart, some blood tests. Also take some pain-killers to get relief from the pain until you get to a physician.
Hope I addressed your concerns.