orthopercussion

Very light percussion of the chest, made in a sagittal direction ( i.e., anteroposteriorly, and not perpendicularly to the wall of the chest); used to determine the size of the heart, with the faint percussion sound disappearing when the heart is reached, even though that may be overlapped by a layer of the lung.

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or·tho·per·cus·sion (or″tho-pər-kushґən) [ortho- + percussion] percussion in which the distal phalanx of the pleximeter finger is held perpendicularly to the chest wall.