β-Blockers can cause bronchospasm in asthma. β2-agonists prolong the QT interval and alter the clinical course of long QT syndrome (LQTS). We report a case of asthma exacerbation treated cautiously with β2-agonists in a patient with LQTS, while LQTS was controlled with low-dose β1-antagonists. A 31-year-old woman with LQTS visited the emergency room for asthma exacerbation. FEV1 was 0.5 L (18%) and QTc interval was 520 ms. Low doses of salbutamol or salmeterol were used and gradually increased, while monitoring the QT interval. Simultaneously, a low dose of atenolol was maintained. FEV1 was increased to 2.2 L (83%) without further QT prolongation or cardiac events. The case suggests that lower doses of β1-antagonists can be tried for cardiac diseases, even in the presence of asthma exacerbations. β2-Agonists may be initiated at lower doses and, if tolerated, the dose can be increased in asthmatic patients with a risk for QT prolongation.