The aim of this study was to investigate the angiographic predictors of exercise induced ischemia in patients with isolated coronary ectasia. We have prospectively analysed coronary angiograms of 1521 consecutive patients undergoing cardiac catheterisation. The overall incidence of coronary ectasia was 6.7% (102 patients). Forty-six patients (3%) with non-obstructive, diffuse or segmental coronary ectasia (i.e. isolated coronary ectasia) constituted the main study group. Coronary angiograms were reviewed for stigmata of an impaired coronary blood flow such as 'slow flow', 'segmental backflow phenomenon' and stasis. 'Slow flow' was quantified with frame counting. An ectasia-jeopardy score was also described in order to assess the effect of the extent of coronary ectasia on exercise induced ischemia. Exercise induced ischemia was observed in 24 patients (52%). Exercise test was abnormal in 70% of the patients with diffuse ectasia and 26% of patients with segmental ectasia (p = 0.003). The frame count of the arteries of the study group was higher than the control group but the correlation between the frame count of the ectatic vessels and exercise induced ischemia was not significant. Stasis of the dye also did not correlate with ischemia. There was a significant correlation between exercise induced ischemia and backflow phenomenon in left anterior descending artery (LAD) (r = 0.56, p = 0.0001). Exercise induced ischemia was best correlated with the ectasia-jeopardy score (r = 0.77, p = 0.0001) and a score of greater than or equal to4 identified the patients at risk with 90% sensitivity and 80% specificity. In conclusion, the extent of the ectasia within the coronary tree, diffuse ectasia and backflow-phenomenon in LAD were identified as the most important predictors of exercise induced ischemia.