7 lines (6 with data), 252 Bytes

m261a 0 128 0 11:10:00 04/01/1991
# Start time=11:10
# First beat=11:18:20.804
# <age-range>: 50-54, <sex>: Male, <medication>: None
# <RR-low-limit(sec)>: 0.406,  <RR-high-limit(sec)>: 1.382
# Note: recording with a timing signal, flutter-compensated