BACKGROUND: Temporal variability in ECG manifestations of cardiac sarcoidosis in patients with documented extra-cardiac sarcoidosis has not been previously reported. METHODS: Six or more 12-lead ECGs were reviewed for each of 8 patients (6 females, 6 African Americans, 38-63 years old) with documented extra-cardiac sarcoidosis. Analyzed ECGs were obtained at intervals no longer than 12 months apart. PR and QT intervals and QRS duration were measured in each ECG lead and averaged for three consecutive beats per lead. The presence of PVCs, AV block, RBBB, and/or QT prolongation was recorded. Between ECG variability was analyzed with ANOVA for continuous data and chi-square analysis for categorical data. RESULTS: Significant variability in ECG indicators of sarcoidosis activity, concurrent with clinical impression of sarcoidosis exacerbation, was detected in seven of eight patients. Most common were new QT prolongation (94%, p=0.031) and PR interval increase (87.5% of the analyzed ECGs, p=0.029). Concordant variability was noted for both in between visit and in between lead comparisons of PR duration, QT/QTc intervals, and QRS duration (p<0.0001 in 5 patients; p<0.001 in 2 patients). No PVCs were documented on the analyzed ECGs. CONCLUSION: ECG abnormalities diagnostic of cardiac sarcoidosis have high temporal variability which parallels clinical impression of extra-cardiac disease activity. A 12-lead ECG is warranted at each visit in patients with documented extra-cardiac sarcoidosis. At the same time, 12-lead ECGs are probably not sufficiently sensitive to detect arrhythmias and/or PVCs in patients with documented extra-cardiac sarcoidosis.