NEW YORK (AP) _ A device that can jolt a fibrillating heart back to normal over the telephone is scheduled for a demonstration in New York on Wednesday, three months after it won government approval.

The MDphone System is aimed at heart patients who are at risk of cardiac fibrillation, in which the heart twitches uselessly because its electrical system has gone haywire.

About 450,000 Americans die of heart attacks annually before ever reaching a hospital, and immediate defibrillation could revive some of the victims, says the maker of the MDphone System, Medphone Corp. of Paramus, N.J.

The system consists of a $7,000 home unit and a $30,000 base station installed at a nearby hospital. When a patient goes into defibrillation, someone else at home is supposed to open the MDphone case and put a pair of chest pads on the victim.

The rest of the work is handled over the phone by the hospital, including monitoring of the heart and, if necessary, triggering of the defibrillator.

Medphone is still negotiating to make its first sales of the device, which was cleared for marketing last December by the Food and Drug Administration. The company says it is in active talks with a number of hospitals.

Medphone said hospitals could charge patients $250 to $300 per month, which would cover the lease or rental of the equipment and the round-the-clock response service. It says hospitals could charge additional fees for interpretation of electrocardiograms and, if necessary, defibrillation.

The main competition for the MDphone System would be implantable defibrillators, which are about the size of a pack of cigarettes, cost roughly $14,000 and have been on the market for about 2 1/2 years.