Irritating errors are called crotchets. This paper discusses the following electrocardiographic crotchets: memorizing patterns rather than using basic principles, failure to use the electrocardiogram as a diagnostic tool, failure to correlate all available data, failure to appreciate the limitation of the computer interpretation, failure to appreciate the diagnostic value of P-wave abnormalities, the identification and misuse of abnormal Q waves, the misuse of left or right axis deviation of the QRS complexes, the misuse of the amplitude of the QRS complexes as a sign of left ventricular hypertrophy, identification of left ventricular hypertrophy, failure to identify uncomplicated and complicated bundle-branch block, failure to identify secondary and primary T-wave abnormalities, failure to identify secondary and primary S-T abnormalities, and lack of knowledge of the U waves.