The effects of coronary pressure on coronary stenosis resistance were studied in 13 open-chest dogs. A noncircumferential stenosis was produced in the circumflex coronary artery by placing sutures into either side of the artery and invaginating a portion of the arterial wall by tying the sutures. Coronary pressure both proximal and distal to the stenosis and coronary flow were measured. Coronary pressure was lowered by 1) hemorrhage and 2) placing a snare proximal to the noncircumferential stenosis and tightening the snare. After hemorrhage, mean proximal coronary pressure fell from 100 ± 5 to 56 ± 6 mm Hg (p < 0.01) and resistance across the noncircumferential stenosis increased from 0.56 ± 0.13 to 1.3 ± 0.26 units (p < 0.05). After the snare was tightened, mean proximal coronary pressure fell from 110 ± 4 to 58 ± 4 mm Hg (p < 0.01) and resistance across the noncircumferential stenosis increased from 0.43 ± 0.05 to 1.1 ± 0.25 units (p < 0.02). In a series of experiments, coronary pressure was raised by inflating a balloon in the proximal aorta. After the balloon was inflated, mean proximal coronary pressure increased from 95 ± 7 to 129 ± 5 mm Hg (p < 0.01) and resistance across the noncircumferential stenosis decreased from 2.34 ± 0.56 to 2.05 ± 0.46 units (p < 0.05). These changes in stenosis resistance were consistent with passive narrowing and distension of the stenotic segment caused by the changes in coronary pressure. Alterations in coronary pressure may therefore affect the severity of a coronary stenosis.