AstraZeneca is to buy Omthera Pharmaceuticals for as much as $443 million to build up its cardiovascular drug business, a priority area for Britain's second-biggest drugmaker.

The acquisition of the U.S.-based specialist in fish oil-derived medicine underscores a drive by new Chief Executive Pascal Soriot to revive AstraZeneca's fortunes through a series of bolt-on deals.

It is his second purchase in the cardiovascular field, following the acquisition last month of AlphaCore Pharma, a small early-stage U.S. biotechnology company.

AstraZeneca's sales and profits are falling as older medicines lose patent protection and the company badly needs new products to replace former blockbusters like the antipsychotic Seroquel, which lost exclusivity last year.

AstraZeneca said on Tuesday it had entered into a definitive agreement to buy Omthera for $12.70 per share, or approximately $323 million, a premium of 88% to Omthera's closing price on Friday.

In addition, Omthera shareholders will get "contingent value rights" (CVRs) of up to approximately $4.70 per share, or $120 million in total, depending on the success of Omthera's experimental drug Epanova, for treating patients with very high triglycerides, a type of blood fat that is bad for the heart.

CVRs are being used increasingly in deals in the pharmaceutical and biotechnology market to bridge differing expectations surrounding new drugs whose final sales are uncertain.

Epanova is an ultra-pure mixture of the free fatty acid forms of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), derived from fish oil. It has already completed final-stage Phase III clinical trials and is set to be submitted for U.S. regulatory approval.

The new drug will compete with other fish oil-based medicines such as GlaxoSmithKline's Lovaza and Amarin's Vascepa. AstraZeneca had, at one stage, been tipped as a possible buyer of Amarin.

Cardiovascular medicine is a key area for AstraZeneca, whose top-selling medicine is cholesterol fighter Crestor. The British-based group said it intended to conduct a series of clinical studies testing a fixed-dose combination of Crestor and Epanova.

AstraZeneca is also banking on another heart drug, Brilinta, to drive sales as older products go off patent.