Note 7—Accrued Warranty

Activity in the product warranty accrual is included in accrued expenses above and consists of the following (in thousands):

Warranty expense was $8,000 and $0.5 million for the three months ended June 30, 2020 and 2019, respectively and $40,000 and $0.8 million for the six months ended June 30, 2020 and 2019, respectively. The accrued warranty balances at June 30, 2020 and December 31, 2019 include $0.1 million and $0.2 million, respectively, relating to the voluntary recall of catheters, which was initiated in September 2019. Warranty expense is included in cost of revenue in the accompanying condensed statements of operations.