Recent research has identified individual differences in interoceptive sensitivity as a key source of variation in action, cognition and emotion. This research has relied heavily on a single method for assessing interoceptive sensitivity: the accuracy of counting heartbeats while at rest. The validity of this method was assessed here by comparing the Heartbeat Counting (HBC) performance of 48 individuals with their Heartbeat Detection (HBD) performance. The Heartbeat Counting (HBC) task required participants to report the numbers of heartbeats counted during brief signaled periods and indexed cardioceptive accuracy based on the difference between the numbers of reported and actual heartbeats. In the Heartbeat Detection (HBD) task, participants indicated the temporal location of heartbeat sensations relative to the onset of ventricular contraction. On each trial they judged whether heartbeat sensations were or were not simultaneous with brief tones presented at one of six fixed delays following R-waves of the ECG. In this method, cardioceptive accuracy or precision was indexed by variability in the temporal location, relative to the R-wave, of tones judged to be simultaneous with heartbeat sensations. Although intra-task correlations indicated that each method yielded reliable scores, inter-task correlations showed that HBC scores were unrelated to HBD scores. These results, which indicate that heartbeat detection and heartbeat counting are distinct processes, raise important questions about the assessment of interoceptive sensitivity and the involvement of this attribute in the psychological processes that have been associated with it on the basis of their correlations with HBC performance.