Objectives To identify the practical heart rate measurement windows by examining the impact of various heart rate ranges on changes in cardiac function in small animal models of health and disease under isoflurane anesthesia using cardiac ultrasonography. Methods Male Sprague–Dawley rats were used to produce a model of post-myocardial infarction heart failure by left anterior descending artery ligation. Each of the model and normal (control) groups included 11 rats. On days 7 and 28 after surger