Voluntary cardio-respiratory synchronization (VCRS) is a technique where an individual's breathing is voluntarily phase locked with his/her heart beat. A signal is generated (tone or light) from the ECG that is used to pace the breath with a fixed number of heart beats for inspiration and expiration. A small portable device was developed that can create a tone to pace the breathing and record the data for repeated measurements for extended periods of time (days or weeks). The device was tested on an individual over a four-week period. Measurements of heart rate variability were made at various times throughout the day for a total of 68 recordings. The data were analyzed to separate out respiratory and non-respiratory induced changes in the heart rate using a unique time domain analysis. The results showed significant variability over the measurement period.