Despite concerns regarding its validity, the two-alternative forced choice heartbeat detection task (2AFC-HDT) is a frequently used measure of cardiac interoceptive accuracy. In this task participants must decide whether a series of tones occur synchronously with their heartbeats. One series of tones is predefined by the researcher as synchronous with heartbeats, and one series predefined as asynchronous. The 2AFC-HDT may result in individuals judged to be not interoceptive when they are, either if participants perceive their heartbeats as occurring synchronously with tones predefined as asynchronous rather than synchronous with their heartbeats, or if they do not perceive either set of tones as synchronous. Currently, there is little data on the proportion of participants this may affect. We addressed this using data from the Phase Adjustment Task (PAT) – a measure of cardiac interoceptive accuracy that determines if, and when in the cardiac cycle, a participant can perceive their heartbeat. The timing of heartbeat perception in 43 interoceptive participants was compared to the timing of synchronous and asynchronous tones used in the 2AFC-HDT assuming temporal precision of 50, 100, and 150ms. Results suggest that between 53.5%-97.7% of delay-based interoceptive individuals perceive heartbeats at a delay that does not correspond to the typical asynchronous or synchronous delays used to present tones on the 2AFC-HDT. These issues suggest that the 2AFC-HDT (or other measures that make assumptions about perceived timing of heartbeats) should not be used to measure cardiac interoceptive accuracy, or cardiac interoceptive insight (also known as awareness or metacognition).