1. Referring to something taking place in uniform time or at regular intervals: All the periods or classes in school were isochronal because each one of them lasted exactly 45 minutes and followed by a break of 10 minutes.
2. Pertaining to things equal in time; contemporary; occurring during the same time: Mary had two clocks with pendulums which were isochronous and swung back and forth at the same time and kept perfect time!

Referring to something occurring at the same time or at a regular time: Sue's heartbeats were always isochronic, because they always beat in a steady and uniform way.

An isochronous pendulum or watch balance has the characteristics of a uniform rate of operation or periodicity.