Myocardial infarction (MI) is a common cause of death due to interrupted blood supply to the heart. Roselle calyx (Hibiscus sabdariffa Linn.) is rich in polyphenols and has a potential in alleviating the risk of cardiovascular disease through its antioxidant activity. This study was aimed to investigate the effects of Hibiscus sabdariffa Linn. or roselle polyphenol-rich extract (HPE) supplementation in oxidative stress and cardiac injury biomarkers as well as cardiac histological changes following isoprenaline (ISO)-induced myocardial infarction (MI). Twenty-one male rats were randomly divided into three groups: control, MI, and HPE+MI. Normal saline or HPE (20 mg/kg BW) was given to MI and HPE+MI groups, respectively, for 14 consecutive days via force feeding. On the 15th and 16th day, 85 mg/kg body weight of ISO was administered subcutaneously to induce MI. Control group was only given normal saline throughout this 16-day duration of study. The results showed that HPE reduced the oxidative stress markers malondialdehyde (MDA) and nitrite oxide (NO) in HPE+MI group when compared with MI group (p<0.05) while increased reduced glutathione (GSH) level reflexes the improvement in antioxidant status. Cardiac injury biomarkers analysis showed no significant difference in HPE+MI group when compared to MI group. Histological study showed that HPE managed to reduce cardiac muscle fibre damage and infiltration of inflammatory cells in ISO-induced MI rats. In conclusion, HPE has the potential in protecting the heart against ISO-induced MI by reducing the oxidative stress and increasing antioxidant status.