MyoKardia, expected to go public this week, is poised to become the next barometer of biotech's status on Wall Street, angling for a $75 million debut as investors take a tepid approach to drug developers. The company, founded by Third Rock Ventures, is at work on treatments for rare cardiac disorders, planning to spend its IPO haul on accelerating its top prospects into clinical development. MyoKardia's planned offering comes amid weeks of sluggish returns for biotechs going public, as the once-bullish market has gradually soured, forcing most recent debutantes to accept cheaper shares and smaller valuations.