A noninvasive radiotelemetry system was developed to monitor heart rates of cows and to view and analyze data. The system was validated by comparing heart rate data of two restrained heifers collected simultaneously using telemetric and direct electrocardiogram measurements and by acquiring data over 72 h from two dry cows housed in an experimental handling facility consisting of a free-stall pen, a holding pen, a pass-through stall, and a second holding pen. Telemetric and direct measurements in response to pharmacological elevation of heart rates were essentially identical. For cows in the experimental facility, peristimulus-time histograms indexed to standing or lying showed that average heart rates for cows increased 4.0 +/- 1.4 beats/min after cows stood and decreased 4.8 +/- 1.0 beats/min after cows lay. Similarly, the average heart rate for the cow naive to the facility increased from 60 to 86 beats/min and remained elevated for 6.3 min when heart rate was indexed to maximal heart rate within +/- 3 min of entry into the pass-through stall. Heart rate for the naive cow increased consistently from around 60 to over 160 beats/min during repeated agonistic encounters between animals. Heart rate for the other cow was not affected by the encounters. These results show clearly that heart rate can be used to monitor animal anxiety.