The Aim is to define the contribution of genetic variation to the interindividual variability in response to β-blockade. The rationale for the study is as follows: Beta-blockers prevent the activation of β-ARs and thus form the cornerstone of treatment of pathological states such as congestive heart failure and coronary artery disease. Functional polymorphisms in cardiac beta-receptors have been shown to determine response to β-blocker therapy. A physiologic stimulus such as exercise causes sympathetic stimulation and activation of the cardiac β-ARs and genotypic differences in response to β-blockers are magnified under states of heightened sympathetic activity. Thus, in addition to measuring the response to β-blockers at rest, we will also determine the response to β-blockade after sub-maximal exercise on a supine bicycle ergometer. Genetic variations that may alter sensitivity to a beta blocker will be sought.