Rotational atherectomy (RA) facilitates stent delivery in highly calcified coronary plaques (CCP). However, lesion ablation by RA in angulated segments may be affected by guidewire bias, leading to a non-uniform plaque modification. Intravascular optical coherence tomography (iOCT) is the highest resolution (∼10 μm axial) intravascular imaging modality available for clinical use; furthermore, near infrared light easily penetrates calcium, with significantly fewer artifacts, including no “blooming effect” as seen by intravascular ultrasound. Therefore, it may pose as a unique tool for serial calcium quantification, as related in this article with pre- and post-RA assessment, allowing accurate characterization of plaque modification, as well as quality of stent deployment. The effects of guidewire bias in the debulking process have not been well documented by iOCT. We present a case of lesion preparation by RA affected by guidewire bias in which iOCT revealed unique insights into CCP modification. © 2011 Wiley Periodicals, Inc.