Echocardiography findings in young lean and obese mice before and after chronic β-adrenergic stimulation. Isoprenaline-filled osmotic minipumps were subcutaneously implanted into 2 months-old WT (n = 12), LepRS1138 (n = 9) and LepRdb/db (n = 7) mice to examine the cardiac response to a hypertrophic stimulus other than leptin. Echocardiography (A-F) was performed immediately before (open bars) as well as at the time of tissue harvest 14 days later (dotted bars). *P < 0.05, *P < 0.01 and ***P < 0.001 for differences vs. WT mice; §P < 0.05 for differences between LepRdb/db and LepRS1138 mice. Significance levels for differences before and after isoprenaline stimulation (as determined using Student’s t test for paired means) are indicated within the graph.