Partial interatrial block (IAB) (P wave ≥110 ms) is a marker of left atrial abnormality. A similar association among patients with advanced IAB (biphasic P waves ≥110 ms in leads II, III, and aVF) is unknown. The authors screened 27 consecutive patients for advanced IAB with transthoracic echocardiograms (TTEs). Of those, 19 who had repeat TTEs after 2 years formed our study cohort. The authors used 44 consecutive controls with partial IAB who had been similarly screened and had follow-up TTEs 2 years apart. TTE parameters were comparable at baseline between groups but were expectedly different on follow-up. When change (delta value) in these indices was compared, however, only left atrial dimension remained significant (advanced 0.07±0.06 mm vs partial IAB 0.03±0.06 mm; P=.03). Further study over a longer duration is warranted to ascertain if advanced IAB patients would benefit from follow-up noninvasive cardiac imaging for appropriate risk stratification.