A device for identifying the likelihood of a patient suffering a myocardial infarction comprises a heart rate monitor operative to generate an output indicative of the current heart rate of the patient, and memory means for storing heart rate data indicative of a heart rate of the patient at which angina has previously occurred. Electronic control means is provided and is operative to analyze both the output from the heart rate monitor and the heart rate data stored on the memory according to an algorithm so as to identify a change in the current heart rate indicative of an increased likelihood of the patient suffering myocardial infarction.