The FDA alerted health care providers to another potential issue with Medtronic's HeartWare Ventricular Assist Device this week, saying a welding defect may cause it to malfunction.

Medtronic notified doctors and health care professionals about the possible defect earlier in the week. The company has an active investigation underway.

Medtronic received three complaints where patients were suspected of having pump thrombosis, a severe complication that can cause a pump to malfunction and is sometimes associated with blood clotting. In all three cases, patients had new pumps implanted.

When the original pumps were returned to the company, it identified a device malfunction in all three. They were manufactured between December 2017 and May 2018.

"We have communicated the potential for this device malfunction to all health care providers with patients on support and have alerted them to the signs and symptoms experienced by patients with the three known affected devices," Erika Winkels, a Medtronic spokeswoman, said in an e-mail.

When the three patients came to doctors, their devices were making abnormal pump sounds, showing excessive power spikes and making patients feel light-headed or dizzy.

"Medtronic has notified, and is working with, all applicable regulatory agencies and authorities on this matter," Winkels said. "Medtronic will share additional information about this issue as it becomes available."

Medtronic stopped selling the HeartWare system last year, but approximately 3,800 patients still have the implanted device.

The company took HeartWare off the market as mounting clinical evidence indicated a higher rate of stroke and death among patients using the product when compared to similar devices.

HVAD was created to help patients with severe heart failure; its mechanical pump was designed to increase blood flow through the body. Medtronic acquired Massachusetts-based HeartWare International in 2016 for $1.1 billion.

A congressional oversight subcommittee is now seeking an investigation into the FDA's oversight of the HVAD system. Last month, U.S. Rep. Raja Krishnamoorthi, D-Ill., sent a letter to the FDA requesting more information about its review of HeartWare's potential problems.