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A 63-YEAR-OLD white male was referred for gated radionuclide ventriculography to evaluate left ventricular reserve and possible wall motion abnormalities during exercise. He had a questionable history of a myocardial infarction 4 years before examination. He had no history of hypertension, diabetes, hypercholesterolemia, or smoking. His family history was also unremarkable. His medications included only salicylates. The patient was evaluated by semiupright bicycle ergometry using one lead for R-wave triggering. A 12-1ead electrocardiogram (ECG) was used to evaluate ST segment changes. Two-minute data acquisitions were attempted during progressive 3-minute exercise stages. The patient exercised for 12.7 minutes to a peak double product of 16,524 and stopped secondary to shortness of breath. The peak heart rate was 102 beats/min, and the actual VO2 was 14.8 mL/kg/min, representing 61% and 55% of predicted maximum, respectively. Blood pressure at rest was normal and increased appropriately during exercise. The ECG at rest showed sinus rhythm with a right bundle branch block. Reduced voltage was also seen in the limb leads. No ST segment or T wave changes were noted after hyperventilation. The patient developed 0.5 mm to 0.75 mm upsloping ST depression in the inferior and anterolateral leads. These changes resolved quickly after exercise and were not diagnostic for ischemia. The patient described no anginal symptoms. The patient's resting ejection fraction was 68% and increased to 79% and 78% during the first and second exercise stages (Fig 1). Using a 10% window for the R-R interval, all beats were accepted during rest; 13 of 143 beats were rejected during the first exercise stage; and 19 of 144 beats were rejected during the second exercise stage. Cornplete data acquisition failure was noted during the third exercise stage as significant ECG artifacts developed (Fig 2). During the postexercise period, the left ventricular ejection fraction was 84%, with 8 of 148 beats rejected. No wall motion abnormalities were noted during the study. A large number of conditions are associated with impaired data acquisition during either resting or exercise gated radionuclide ventriculography. These conditions can be divided into two groups: (1) those associated with R-R interval variability and (2) those associated with increased P or T wave amplitude or with reduced R wave amplitude. The approach to data acquisition will differ with each of these conditions. When R-R variability arises, variable windowing or list mode acquisition (when available) may be helpful. When altered P, R, or T wave amplitude is present, lead repositioning (not possible during exercise) or altered R wave trigger thresholds may be helpful.