Shares of CVRx fell after the company cut its sales outlook, citing a prolonged issue with one of its biggest customers.

The stock sank 42% to $3.44 in premarket trading Friday. Through the previous close, shares were down 16% this year.

The commercial-stage medical device company lowered its guidance for full-year revenue to a range of $58.0 million to $60.0 million, from $63.0 million to $67.0 million previously.

It expects to record $13.5 million to $14.5 million in sales during the current third quarter, which would be below the $15.6 million analysts are projecting, according to FactSet.

Chief Executive Kevin Hykes said he wasn't satisfied with the lower sales outlook. The guidance cut was driven by fewer sales territories than anticipated, lower sales force productivity and a prolonged challenge with one of CVRx's biggest players, he said.

CVRx's loss was also wider than expected at 53 cents a share, compared with analysts' estimate of a 51-cent loss per share.