Ten patients underwent myocardial scintigraphy with 123I-iodo-heptadecanoic acid (HDA), which was injected in the last minute of maximal exercise testing. Six of the patients were rescanned following percutaneous transluminal coronary angioplasty. All ten patients underwent full coronary angiography. There were visible perfusion defects on the static images in 74% of the myocardial areas which were supplied by an artery with a stenosis greater than 75%. The mean half life recorded from areas distal to an arterial stenosis of at least 90% (35.69 min +/- 41.25 min), was longer than the expected normal mean (18.85 min +/- 3.35 min). However, the difference was not statistically significant. The static images changed in some patients following angioplasty, however there was no consistent alteration in the half lives. It was concluded that HDA is a suitable agent for investigating myocardial perfusion, but that the half life cannot be measured adequately for clinical purposes with a planar imaging system.