Active implantable medical device such as pacemaker, defibrillator and/or cardiovertor of type AAI or AAI/DDD, with ventricular tachycardia detection means

The device has a detecting unit detecting spontaneous atrial and ventricular events, and a unit delivering an atrial stimulation pulse. An application unit applies a refractory period (PR) and a safety window (FS) of a preset duration, to the detecting unit. A determination unit determines the start of a spontaneous ventricular cycle in response to the detection of ventricular events outside the safety windows. A detection unit detects ventricular tachycardia in response to the detection of ventricular events inside and outside the safety windows.