Various causes. Depends on where in the groin. The femoral artery and femoral vein run right on top of the groin where the leg and torso connect. Lumps with heart beat could be aneurysm, or contained bleed- both unusual. Also a lymph node. Lump near scrotum has various causes. You need a doc eval for this and may need an ultrasound of this lump. Sometimes need to examine tissue of these to make sure not a cancer.