7 lines (6 with data), 252 Bytes

m274a 0 128 0 10:30:00 20/12/1990
# Start time=10:30
# First beat=10:38:16.757
# <age-range>: 65-69, <sex>: Male, <medication>: None
# <RR-low-limit(sec)>: 0.476,  <RR-high-limit(sec)>: 0.984
# Note: recording with a timing signal, flutter-compensated