BACKGROUND Many adults with repaired tetralogy of Fallot have had prior Blalock-Taussig shunts. These shunts may theoretically hinder growth and development of the ipsilateral arm. METHODS We prospectively enrolled consecutive patients with tetralogy of Fallot in a cross-sectional study to measure arm length and assess handgrip strength. Bilateral handgrip strength was quantified by a dynamometer in a standing position after instructing patients to clench each hand tightly in succession. The maximum force achieved, in kilograms, was measured. RESULTS A total of 80 consecutive adults with tetralogy of Fallot, aged 36.0 ± 12.5 years, 49% female, were prospectively enrolled. Thirty-eight (47.5%) patients had prior Blalock-Taussig shunts at a median age of 1.0 year. Twenty-one (55.3%) were left-sided and 23 (60.5%) were classic shunts. All but six patients with right-sided shunts and one without a prior shunt were right-handed. The shunts were present for a median of 4.0 years prior to takedown during corrective surgery. The arm ipsilateral to the shunt was significantly shorter than the contralateral arm (71.5 ± 6.1 versus 73.6 ± 5.6 cm, P<0.0001). Handgrip strength was significantly weaker on the ipsilateral versus contralateral side (median [IQR], 26.5 [14.0-41.5] versus 31.0 [18.0-46.0] kg, P<0.0001) and the ipsilateral-to-contralateral handgrip ratio was lower with classic versus modified shunts (median [IQR], 1.05 [1.02-1.14] versus 1.19 [1.07-1.33] kg, P=0.0541). CONCLUSION In patients with tetralogy of Fallot, Blalock-Taussig shunts may impair normal development of the ipsilateral arm with repercussions in adulthood that include shorter limb length and reduced handgrip strength. These changes are most pronounced in patients with classic end-to-side anastomoses.