An innovative natriuretic peptide analog named CNAAC (structurally consisting of the C-terminus and ring of ANP and the N-terminus of CNP) that has been shown to exhibit potent vasodilatory, diuretic, and hypotensive effects in our previous study was evaluated for the treatment of left ventricular dysfunction following myocardial infarction. The temporal relaxation effect and metabolic status of CNAAC were determined. A myocardial ischemic model was established. Rats were randomly divided into Sham, MI, MI-ANP, MI-CNP, MI-VNP, and MI-CNAAC groups. Humoral factors were measured; echocardiography and hemodynamics methods were employed to assess the cardiac function at the fourth week after modeling. The results showed that CNAAC had a potent relaxant effect and longer duration of action than ANP, CNP, or VNP. The stability of CNAAC in blood was higher than other three NPs. Four weeks of NP administration ameliorated diastolic and systolic dysfunction, the hypertrophic index, myocardial fibrosis, and infarct size; it also restored the abnormal changes in humoral factors. These results demonstrate that CNAAC has a potent cardioprotective effect against left ventricular dysfunction after myocardial infarction. The results may lay the foundation for the clinical application of this newly designed NP chimera in the treatment and prevention of heart failure.