Pectoralis muscle uptake of thallium-201 after arm exercise ergometry. Possible confusion with lung thallium-201 activity.

Pectoralis muscle uptake of thallium-201 was noted in 8 (73%) out of 11 patients after exercise arm ergometry. Uptake varied from mild to marked and potentially could be confused with pulmonary Tl-201 activity with a resulting false-positive diagnosis of exercise-induced left ventricular dysfunction. The three patients exhibiting negative or trace Tl-201 uptake had suboptimal exercise efforts. The characteristics of pectoralis muscle Tl-201 uptake are illustrated, and differentiation from true lung Tl-201 activity is discussed.