Abstract We have assessed the impact of cardiovascular nuclear medicine studies (CVNMS) on physicians' decisions to send patients with suspected ischemic heart disease ( N = 439) on to cardiac catheterization at three Bronx hospitals. A change in management plans with respect to catheterization was observed in 31% of cases. Catheterization rates were reduced by 25% among patients referred for resting studies and by 49% for exercise studies (thallium perfusion or exercise wall motion studies). Results of CVNMS had little impact on catheterization decisions for resting study patients ( N = 192). Among exercise study patients ( N = 247), those with normal results had a relative reduction in catheterization post-CVNMS of 82% vs 27% for patients with abnormal results ( p < 0.001). However, impact of exercise CVNMS test results on post-CVNMS catheterization rates obtained for men only; women with abnormal exercise study results were much less likely to undergo subsequent catheterization (7.7%) than men with abnormal results (41.9%), p < 0.005, independent of age. The apparent discrepancy in referral for catheterization based on sex needs to be investigated further.