3-4 months baby with heart rate 250/min, QRS complex less than 0.07 sec and no P wave, Diagnosis will be :

SVTs are the most common symptomatic arrhythmias in all children including neonates. SVTs usually have Rate > 200 beats/minute Normal or narrow (<0.07 sec, A wide QRS > 0.07 sec favors diagnosis of ventricular tachycardia). Ventricular complexes on the surface ECG.