Modern therapy for both cardiovascular disease and obstructive lung disease involves diametrically opposed manipulations of the beta-adrenoceptor. Beta-agonists reduce airflow limitation and improve symptoms among patients with obstructive lung disease while beta-blockers reduce symptoms, recurrent myocardial ischaemia and all-cause mortality among patients with ischaemic heart disease. There is biological plausibility for beta-agonists leading to adverse cardiovascular outcomes, and observational trials have raised concern about the safety of beta-agonists among patients with cardiovascular disease. Although there are many potential causal and noncausal explanations for these observational findings, the implications from these studies are the same. Physicians should be careful when prescribing beta-agonists for patients at risk for ischaemic heart disease. Furthermore, careful consideration should be given to distinguish symptoms caused by cardiovascular versus respiratory aetiologies.