I. Introduction
As per the records of World Health Organization (WHO), cardiovascular disease (CVDs) or also known as heart disease is the leading cause of death. It is a dangerous illness and a worldwide invisible killer that claims over 17.8 million people in the year 2017 [1]. In Malaysia, heart disease is the main cause of mortality [2]. According to China’s annual report on cardiovascular health and disease, CVDs mortality in rural and urban areas was 45.50% and 43.16% respectively, in 2016. Nonetheless, the CVDs mortality rate has risen [3]. There is no denying that early detection is critical in preventing this disease as well as reducing the mortality rate. Meanwhile, Electrocardiogram (ECG) and cardiac Magnetic Resonance Imaging (MRI) are commonly used in hospitals and clinics to identify this disease. However, these methods have not been influential due to their high cost and lack of portability. Conversely, previous researchersh has established that a phonocardiogram (PCG) signal can be utilized for this disorder. Phonocardiography is a non-invasive, quick and low-cost diagnostic technique that can be used for detecting and recording heart sound. Heart sounds is generally reorganized into four components, which is labelled as S1 which corresponds to first normal sound; S2 representing second heart sound; S3 which describes third heart sound for abnormalities; and S4 for fourth abnormal heart sound. The two common normal heart sounds are S1 and S2, namely a lub and a dub respectively [3]. In contrast, the S3 and S4 are abnormal heart sound components that use to signal cardiac failure during the diastolic period [4]. Most studies in the fields of PCG signals have only investigated the two primary components, S1 and S2 due to the onset of ventricular contraction and the end of ventricular systole respectively [5].