Unamba, Norbert Ndubuisi, et al. “The Functional Class and Electrocardiographic Abnormalities in Heart Failure Patients in Southern Nigeria: A Retrospective Observational Study”. The Nigerian Health Journal, vol. 20, no. 2, Oct. 2020, pp. 44-53, https://tnhjph.com/index.php/tnhj/article/view/475.