Cardiovascular diseases (CVDs) are very common in modern society, such as atherosclerosis, hypertension, etc., which have a great impact on heart function. Therefore, hospitalization monitoring alone is far from enough. Long-term monitoring of the heart is needed in daily life. The technology of non-invasive monitoring of the cardiovascular system can meet the needs of long-term monitoring of the heart condition, helping to promote the improvement of lifestyle and daily care, reducing the overall risk of developing CVDs. The purpose of this study is to investigate the cardiac response after different exercises using a 3 x 3 demodulation scheme-based ballisto-cardiography (BCG) monitoring system. A fiber optic sensor (FOS)-based smart cushion is used to replace the traditional inconvenient electrocardiogram (ECG) for heart rate variability (HRV). The correlation between BCG inter-beat interval (IBI) and ECG IBI is 0.9862, and the RMSE is 0.0139. The BCG signal can assess cardiac contractility by analyzing RJ interval with ECG, which is a practical alternative to the pre-ejection period (PEP).