BACKGROUND The aim of the study is to contrast the role of conventional ambulatory electrocardiographic monitoring (AEM) artifacts with a less emphasized problem with potentially more serious implications, that is, the failure to recognize, and therefore misinterpret, a genuine arrhythmia episode in the AEM recording. METHODS The study material included 500 Holter recordings and 500 recordings from the cardiac telemetry unit. RESULTS Electrocardiographic (ECG) artifacts were more common in telemetry recordings (5.6%) compared to Holter recordings (4%) for a total of 4.8%. There were 35 examples of misinterpretation of AEM recordings (3.5%). These were significantly more common in telemetry recordings (2.6%) compared to Holter recordings (0.9%). The most common ECG artifacts were examples of pseudo ventricular tachyarrhythmia (VT). The majority of misinterpretation (26 of 35 examples) were fast supraventricular tachyarrhythmias with aberrant QRS (including six examples of atrial flutter with periods of 1:1 atrioventricular conduction) that were misdiagnosed as ventricular VT. Other examples were misinterpretation of arrhythmic episodes consistent with sick sinus syndrome, pacemaker malfunction, and long QT syndrome. Only 5 of 48 examples of AEM artifacts resulted in management errors of commission or errors of omission compared to all 35 examples of misinterpretation. CONCLUSIONS Compared to conventional artifacts in AEM, misinterpretation of nonartifactual arrhythmic episodes consistently resulted in management errors. Misinterpretation was significantly more common with telemetry recordings compared to Holter ECG. This highlights the need for more appropriate training of the entire clinical team in charge of the management of the cardiac telemetry unit.