The purpose of this study was to determine whether the capillary transfer constant (Ki) of gadolinium-DTPA was sensitive to perfusion changes and whether ischemic regions in the myocardium could be identified using the modified Kety formula. Ki was measured at rest and during dipyridamole-induced vasodilation in 10 healthy volunteers and in 10 patients with ischemic heart disease. Ki increased by a factor of 2.5+/-1.2 (mean +/- SD) from 55+/-16 ml 100 g(-1)min(-1) at rest to 136+/-46 ml 100 g(-1)min(-1) (P < 0.01) during vasodilation in the healthy subjects. In the patients, there were no changes in Ki during vasodilation in ischemic regions (50+/-18 versus 49+/-30 ml 100 g(-1)min(-1) (P > 0.4)). Ki increased in nonischemic regions by a factor of 2.0+/-0.8 from 44+/-17 to 81+/-32 ml 100 g(-1)min(-1) during vasodilation (P < 0.02). It is concluded that the capillary transfer constant is sensitive to perfusion changes and that regional ischemia can be detected with MRI. This noninvasive and quantitative method may prove useful in the evaluation of patients with ischemic heart disease.