Percutaneous transluminal coronary angioscopy was performed during routine coronary angiography in seven patients and during PTCA in one patient with ischemic heart disease. A flexible fiberscope with an external diameter of 1.4 mm was introduced through an 8F or 9F guiding catheter used for PTCA into the coronary arteries. Warmed saline solution (15 to 20 ml) was injected through the guiding catheter into the coronary arteries for replacement of blood. Twenty-one of the 31 coronary segments were visualized and photographed on color cinefilms. The lumen of the atherosclerotic segment showed narrowing with smooth surface or with spiral folds. PTCA caused dilatation of the stenosed segment with scattered thin thrombi. These findings indicate the usefulness of angioscopy to observe luminal changes in the coronary arteries of patients with ischemic heart disease.