In addition to the sustained arrhythmias described above, isolated ventricular and supraventricular ectopic beats are also quite common. Ventricular ectopic beats are recognized as wide bizarre QRS complexes which occur prematurely and are not usually preceded by a P wave. Sometimes a late diastolic ventricular ectopic can occur just after the P wave. If ventricular ectopics are very frequent or occur very prematurely so as to fall on the T wave of the previous beat, they can lead on to ventricular tachycardia or fibrillation. Isolated ventricular ectopic beats without any associated structural heart disease are usually left alone. Supraventricular ectopics are premature narrow QRS beats resembling the sinus beats. The P waves have a different morphology compared to the sinus beats or may be absent in case of junctional ectopics. Suprventricular ectopy may indicate atrial dilatation as in left ventricular dysfunction and is a reason to suspect the latter in those with structural heart disease.