However, under cardiac stress conditions induced by isoproterenol injection, the Cd69–/– mice had an enhancement of the above-mentioned cardiac arrhythmias compared with their wild-type littermates, and, eventually, bradyarrhythmias led to complete heart block, ventricular escape rhythms, and death (Supplemental Figure 2). The gene discussed is CD69; the disease is chronic obstructive pulmonary disease.