A non-invasive cardiac monitoring device for calculating the cardiac performance parameters of heartbeat, stroke volume, and cardiac output for an individual. The device receives a plurality of electrocardiogram waveform signals from the individual and selects the R-wave component having the maximum value of the electrocardiogram waveform signals and the T-wave component having the maximum value of the electrocardiogram waveforms. From these values, the stroke volume of the individual and the cardiac output of the individual may be calculated according to the equation: Stroke Volume=6.times.R(max.)/T(max.)+26.0. The periodicity of subsequent electrocardiogram waveforms are utilized to calculate the cardiac performance of the individual.