The classical music world is full of stories about great musicians suffering heart attacks in mid-performance but soldiering on because the repertoire was so great they didn't want to stop.

Nothing of that sort was going to happen Sunday at First Unitarian Church of Philadelphia when Richard Reed Parry, best known as a member of the Arcade Fire collective, arrived on a tour supporting his first solo album, Music for Heart and Breath. Released by the classical label Deutsche Grammophon, the disc (or discs if purchased on LP set) consists of his own compositions, requiring all participating musicians to wear a stethoscope, and to play with tempos dictated by their heartbeat and breath.

A lovely idea, directed at getting at fundamental impulses that Parry says he found were missing with much of the music he heard as a younger musician - and the polar opposite of his indie rock music with Arcade Fire. So fans of that popular alternative-rock band might have been a tad bewildered by the quiet, delicate music heard on Sunday.

The works - titles included Quartet for Heart and Breath, Heart and Breath Sextet, and a long suite called Interruptions - had varying instrumentation (strings, brass, keyboard, and, in one piece, piano with three simultaneous players) but were similar in character. Parry has his own personalized style of minimalism reminiscent of Arvo Pärt combined with ambient-music masses of sound, sometimes with the two elements stated in opposition to each other and moving toward resolution.

The role of the stethoscope may be overplayed, partly because the musicians left one ear free, presumably for the purpose of listening to themselves and those around them. The yMusic ensemble, including starry sidemen such as pianist/composer Nico Muhly, had fairly uniform heartbeats. So their moments of somewhat divergent rhythm gave an attractive sway to the music. Mostly, the stethoscopes seemed to make the difference between a chord played in strict synchronicity and one with each of the voices individually articulated, played as an arpeggio. Parry has stated that he wants heart and breath to run gentle interference with the conservatory background of the musicians at hand. But the dividends paid to listeners aren't that great, once one has the basic idea.

More entrancing was the opening act, a half-hour ambient-oriented improvisation by harpist Mary Lattimore and electronic musician Jeff Zeigler, both creating a variety of overlapping sounds that were delayed and looped in dreamy, poetic ways with surprising coherence and continuity. They're local. Support them.