This paper reports recent investigation on the possibility of human cardiac motion imaging using a continuous-wave microwave Doppler radar sensor. Compared with existing works of vital sign radar sensors that mainly focused on the heartbeat rate, the challenge is detect the actual pattern of cardiac motion. To achieve this, a DC-coupled direct conversion architecture and a digital-IF architecture can be used because both of them can avoid frequency-dependent signal distortion. A digital-IF Doppler radar sensor employing an extended differentiate and cross-multiply (DACM) algorithm was adopted to perform a series of experiments that investigate the effectiveness of noncontact cardiac imaging from different orientations of a subject. Experimental results demonstrated that in addition to detecting heartbeat rate, Doppler radar could also image one-dimensional, time domain cardiac motion that fits well with the known physiological description.