Coronary air embolism is one of the inadvertent complications of coronary angioplasty. We report two rare cases of complicating air embolism in the right coronary artery occurring during control left coronary angiography using a guiding catheter with a side hole, just prior to a coronary intervention procedure for a left coronary artery lesion. The air seemed to be injected into the right coronary artery through the side hole. When we use an angiographic or guiding catheter with a side hole, we should be aware that an air embolism can occur in the contralateral coronary artery and should carefully and repeatedly perform aspiration of the catheter.