A lightweight portable probe or transducer containing a transmissive or reflective electro-optical emitter and receptor in the infrared spectrum is fitted on a subject's finger or toe. Associated electronics energize and monitor the probe, detect cardio-rhythmic fluctuations therefrom, and process digital data over a prescribed window to produce a non-invasive, qualitative or quantitative measure of the subject's circulation. In accordance with one embodiment of the invention, a simple tri-color LED array is used to indicate the subject's circulation as being normal, reduced, or borderline.