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Figure 1 Examples of the normal and increased right ventricular (RV) activity are shown. (A) Mid-ventricular horizontal long axis and short axis images are shown in a normal participant at exercise (above) and rest (below). There is a normal degree of RV activity at stress (arrow). The resting scan shows normal RV activity, but with some splanchnic thallium-201 activity that limits the evaluation of the counts in the inferior aspect of the RV. (B) These images are from a patient with left main and three-vessel CAD, but only mild CAD in the proximal right coronary artery. The resting images are normal. With exercise, there were only mild reversible perfusion abnormalities (anterior, inferolateral, lateral-apical, lateral), but exercise-induced ischemic cavity dilatation, consistent with more global ischemia. The relative RV activity was normal at rest, but increased markedly with exercise, consistent with global LV ischemia, preserved RV perfusion, and most possibly an increase in pulmonary pressures with stress. (C) These images were obtained on an elderly patient with an ostium secundum atrial septal defect, severe pulmonary hypertension and marked RV hypertrophy. The increased RV activity is present at rest and stress (RV:LV activity indexes of 0.51 and 0.53, respectively) with a normal exercise to resting ratio of 1.045. CAD = coronary artery disease; LV = left ventricular; RV = right ventricular.