A mobile electrocardiogram (ECG) transmission system was developed which could transmit single-lead ECG data via GSM mobile telephony. Ambulance transmission trials comprised a total of 72 communications, of which 94% were successful. The system was able to redial up to a predetermined number of times until the GSM call was re-established (during the trials this value was set to five). The average number of GSM call tries was 1.3 per connection. The mean time required to establish a connection was 45 s; the minimum was 34 s, when only one attempt was needed to establish a GSM call. The average duration of ECG transmission between communication breakdowns was 5 min 12 s. When a link breakdown occurred, the user had to wait for an average of only 42 s to continue monitoring the signal.