We analyzed the heartbeat interval to test the possibility that the detrended fluctuation analysis (DFA) distinguishes a sick condition from a healthy condition of the cardiac control network. The healthy heart exhibited exponents ranging from 0.8 to 1.0 in both, animal models and humans. In the sick animal models, the exponents declined with an approaching very low range leading to a natural death (~0.6 in the end). Other models, which had a myocardial injury, exhibited extremely high exponents (~1.4). The high exponent was maintained until they died. Human arrhythmic hearts exhibited low exponent (~0.7). A human subject who has an abnormally high heart rate exhibited high exponents (as high as 1.4). A Human transplanted heart, which has no nervous controls, exhibited exponent 1.2. The fluctuation of the heartbeat interval contains information for the risk of a cardiac cessation or mortality.