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Background: Transient arrhythmias can affect transient ischemic dilation (TID) ratios. This study was initiated to evaluate the frequency and effect of normal heart rate change on TID measures in routine clinical practice. Methods: Consecutive patients undergoing stress/rest sestamibi gated myocardial perfusion scintigraphy were studied (N = 407). Heart rate at the time of stress and rest imaging were recorded. TID ratios were analyzed in relation to absolute change in heart rate (stress minus rest) for subjects with normal perfusion and systolic function (Group 1, N = 169) and those with abnormalities in perfusion and/or function (Group 2, N = 238). Results: In Group 1, mean TID ratio was inversely correlated with the change in heart rate (r = 0.47, P < 0.0001). For every increase of 10 BPM in heart rate change, the TID ratio decreased by approximately 0.06 (95% confidence interval 0.04–0.07). In Group 2, multiple linear regression demonstrated that the change in heart rate (beta = -0.25, P < 0.0001) and the summed difference score (beta = 0.36, P < 0.0001) were independent predictors of the TID ratio. Conclusion: Normal variation in heart rate between the stress and rest components of myocardial perfusion scans is common and can influence TID ratios in patients with normal and abnormal cardiac scans. Background The assessment of myocardial perfusion with radioactive flow tracers provides valuable clinical information for diagnosis and risk stratification [1-3]. Individuals with normal myocardial perfusion during an adequate stress procedure are generally regarded as being at low risk for major cardiac events [4,5]. In addition to perfusion, a number of ancillary functional parameters can be extracted from these images [6]. These have been shown to provide additional prognostic information that is additive to the clinical and perfusion data alone. For example, left ventricular systolic function can be assessed with gated single photon emission computed tomography (SPECT), left ventricular cavity size can be measured, and lung uptake measurements can be computed [7-11]. Each of these parameters has been shown to provide incremental prognostic information. "Transient ischemic dilation" (TID) of the left ventricular cavity is a marker of severe coronary artery disease and Published: 11 January 2007 BMC Nuclear Medicine 2007, 7:1 doi:10.1186/1471-2385-7-1 Received: 20 November 2006 Accepted: 11 January 2007 This article is available from: http://www.biomedcentral.com/1471-2385/7/1 © 2007 Leslie et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.