X ray coronary angiography has become an indispensable technique for assessing coronary heart disease. However, repeated angiography causes various complications in some patients. We evaluated coronary stenoses non-invasively, before and after percutaneous transluminal coronary angioplasty (PTCA), using magnetic resonance coronary angiography (MRCA). Twenty-four patients underwent MRCA and PTCA. MRCA was performed using a gradient echo sequence with K-space segmentation. MRCA images were classified as normal, vessel narrowing, reduced intensity, breakage of vessel and inability to image. MRCA performed before PTCA showed abnormal findings in ail patients (reduced intensity in five, vessel narrowing in four, breakage of vessel in 13, inability to image in two). Although every patient underwent successful PTCA, MRCA performed after PTCA showed abnormal findings (reduced intensity in seven, vessel narrowing in five) in half ti-ie patients. Patients who had complex lesions had a tendency to exhibit abnormal findings in MRCA. MRCA provided useful information parallel to X ray angiography before PTCA. However, after successful PTCA, it still showed abnormal findings in half the patients. it was considered that MRCA over-estimates medium stenoses. and was difficulty imaging complex lesions or tortuous vessels. It was concluded that MRCA has potential as a non-invasive examination technique to image coronary arteries before and after PTCA.