The heart is on the left usually, but we apply compressions on the sternum, because it is strong enough to stand up to the compressions. Nothing to do with which side the heart is on. Should still work for a heart that is on the left or the right. Ribs commonly get broken during CPR, you are warned about that in training, and that is why you do NOT do compressions directly over the heart. Source: have been both red cross and green cross certified in CPR.