Chronic injection with the β‐adrenergic receptor (β‐AR) agonist isoproterenol (ISO) has been commonly used as an animal model of β‐AR–induced cardiac remodeling and heart failure. This ISO‐treated model usually shows significantly decreased conscious heart rate (HR). However, the HR in treatment groups is usually adjusted to the same levels by anaesthesia to assess cardiac geometry and function. Here, we reveal a method of echocardiography assessment that represents the true cardiac geometry and function. C57BL/6 mice received 5 mg/kg/day ISO for 12 weeks. Cardiac geometry and function were assessed by high‐resolution echocardiography in vehicle‐ and ISO‐treated mice under conscious or varied anesthetic conditions. Cardiac β‐AR response was decreased in ISO‐treated mice, as evidenced by markedly decreased conscious HR. Vehicle‐ and ISO‐treated mice did not differ in cardiac geometry or function when HR was adjusted to the same level (400 beats/min) in both treatment groups but did differ when using a low (1%) rather than high (1.5% or 2%) isoflurane concentration for HR adjustment. Furthermore, 3‐day ISO withdrawal eliminated the difference in conscious HR between the 2 groups. Also, the groups differed in cardiac geometry and function values regardless of isoflurane concentration. Use of isoflurane to decrease HR of treatment groups to the same level may mask the left‐ventricular dysfunction of ISO‐treated mice. Therefore, we demonstrate that ISO withdrawal eliminates the interference of different basal HR between treatment groups on echocardiography measurements, allowing a more accurate assessment of cardiac pathological and functional changes. This article is protected by copyright. All rights reserved.