The bullishness has taken shape since April 18, when THOR gapped higher amid news that a rival's products caused potentially fatal blood clots. Management also raised guidance the last time earnings came out on Aug. 3.
Friday's option activity focused on the October 35 calls, with about 2,000 contracts purchased for $0.90 to $1.10, according to OptionMonster's real-time tracking systems. The stock closed down 1.6 percent to $32.64, so those traders are looking for a rally of at least 10 percent in the next three weeks. Volume was 8 times open interest in the strike.
More than 2,400 calls traded in the session versus less than 60 puts. Total options turnover was 900 percent greater than average.
Second Opinion: A Thoratec Pop...Will It Last?
—Russell has no positions in THOR.
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David Russell is a reporter and writer for OptionMonster.