A patient sustains a knife wound through the right fourth intercostals space, 2 cm to the right of the sternum. The area most likely penetrated by the knife is the

The right border of the heart is approximately 1 to 2 cm to the right of the right border of the sternum; therefore, the knife probably did not hit the heart. The middle lobe of the right lung extends from the level of the fourth costochondral junction to the level of the fifth intercostal space. The middle lobe is most likely at the level of the fourth intercostal space.