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This paper presents an experimental investigation that demonstrates the possibility of 1-D imaging of human cardiac motion using a microwave Doppler sensor. Compared with the previous works that primarily monitored human respiration and heartbeat rates, the reconstruction of cardiac motion in this work will provide more information for time-domain clinical diagnosis. To fully recover the motion information from the backscattered microwave signal, an instrument-based digital-IF Doppler radar sensor employing a dc-offset removal and an extended differentiate and cross-multiply algorithm was used. A series of experiments were performed to investigate the effectiveness of the cardiac imaging from different orientations of a subject. Analysis on the experimental results indicates that in addition to the respiration and heartbeat rates, a 1-D time-domain cardiac motion that fits well with the known physiological description can be obtained. Our work reveals that substantial cardiac activity information is carried by the Doppler shifts of the backscattered microwave reflected from a human chest. The information can be reconstructed by properly designed hardware and algorithms. The possibility of noncontact cardiac imaging would have a great potential in clinical diagnosis and treatment of human heart diseases.