Cardiovascular diseases are among the most common causes of death in industrial countries. In order to take preventive actions, it is of great interest, to both physicians and patients, to determine cardiovascular risk factors early. To address this problem, a wearable in-ear measuring system (IN-MONIT) for 24/7 monitoring of vital parameters has been developed. The central component is a microoptic reflective sensor located inside the auditory canal. From the measured photoplethysmographic curves, heart activity and heart rate can be derived. In this paper, we describe the optoelectronic sensor concept and the autonomous design of the IN-MONIT measurement system. For the assessment of heart rate, different algorithms are introduced and the performance of the developed sensor system is evaluated in relation to conventional systems. In addition, the robustness to external artifacts is evaluated and artifact reduction strategies are considered.