We evaluated the functional significance of angiographically successful percutaneous transluminal coronary angioplasty (PTCA) in 50 patients before and after PTCA using an atrial pacing stress test. Before balloon angioplasty, 40/50 patients had transient ST-segment changes on the intracoronary (IC) ECG. After PTCA 14/50 patients continued to have ischemic changes on IC-ECG. Atrial pacing stress tests can be performed easily in the cardiac catheterization laboratory. Despite angiographically successful dilatation, 28% of the patients have inducible ischemia indicating functionally inadequate dilatation. Inadequate functional dilatation may contribute to early return of symptoms in some patients.