RESUMO
INTRODUCTION: Left bundle branch block (LBBB) disrupts the electrical activation of the left ventricle, potentially impairing its systolic function, leading to LBBB-induced cardiomyopathy. This study examined cardiopulmonary exercise test (CPET) variables in patients with and without LBBB and assessed the longitudinal development of left ventricular ejection fraction (LVEF). METHOD: An observational, comparative clinical study was executed in two stages at a private hospital in Brazil. The sample consisted of 27 individuals: 11 with LBBB and 16 without LBBB, all with preserved LVEF (>50%) and without confirmed ischemia. CPET variables were assessed, and after 4 years, participants had a transthoracic echocardiogram for LVEF re-evaluation. Groups were compared using the t test or the χ2 test. Multivariate analysis of covariance determined effect magnitude. RESULTS: Patients with LBBB demonstrated significant differences in CPET variables, particularly in predicted peak