The helicopter transport of acute cardiac patients has become increasingly common, although no study has examined solely the effect of such transport on outcome in this subset of patients. A combined air and ground critical care transport service provided the opportunity for a direct comparison of patients with acute cardiac conditions (myocardial infarction or unstable angina) transported either by our helicopter or by a specially equipped critical care ground vehicle. Both air and ground components were similarly equipped in terms of personnel and medical equipment. Seventy-eight (27 ground, 51 air) transport cases were studied. Both patient groups were comparable in terms of age, sex, Killip classification, and diagnosis. Serious untoward events, defined as arrhythmias, chest pain, hypotension, bradycardia, seizures, and cardiac arrest, occurred in 41% of air transports and 7.5% of ground transports (P less than .002). The overall incidence of untoward events was also significantly greater with air transports (25/51, or 49%) than with the ground vehicle (4/27, or 15%; P less than .005). The reasons for these differences are unknown.