The review is structured in such a way as to fall naturally into four main sections. These are as follows: clinical overview of the common mechanisms leading to the generation of tachyarrhythmias; commonly used sensing techniques and algorithms for the detection of tachyarrhythmias; electrical stimulation algorithms used to terminate many of the rhythms; existing implantable devices and a brief look at the future. The clinical overview introduces the reader unfamiliar with tachyarrhythmias to such mechanisms as sinus tachycardia, supraventricular tachycardias (SVTs), ventricular tachycardia, 'torsade de pointes', and ventricular fibrillation. SVT includes paroxysmal SVT, atrial flutter, atrial tachycardia and junctional tachycardia (enhanced automaticity). Also there is a brief introduction to alternative therapies (drugs, surgery etc.) The sensing techniques section covers input signal processing to enable the R wave to be adequately detected; while the tachycardia detection algorithms section discusses such areas as simple rate detect, rate of change of rate detect, stability of rate, the so-called probability density function technique and some other more complex detection algorithms. The section on electrical stimulation algorithms used for tachycardia therapy discusses burst pacing techniques, special cases such as automatically decrementing bursts and automatically incrementing bursts, defibrillation shock therapy (since fibrillation is a form of tachyarrhythmia) and several other more complex algorithms. The review finishes up with a discussion of current implantable antitachy pacemakers and defibrillators. There is also a speculative look at the future to enable the reader to obtain a full picture.