The normal flow values through healthy or moderately narrowed coronary arteries, which had been determined by a new method of cine radiography, together with a computer, were published in this Journal in 1976. In the present paper we report the results of further studies of flow velocity and flow volume through high-grade coronary artery stenosis of severity III and III--IV. Compared with the results obtained on normal and mildly stenosed arteries, measurements at rest through severely stenosed coronaries showed an almost constant flow. The first results on aorto-coronary vein graft measurement are described.