It is the aim of the study to compare the effects of 6 weeks of either high-intensity interval training (HIT; carried out at correctly assessed 85-95% of maximal heart rate), pyramid, or continuous endurance training, on changes of physical exercise capacity in cardiac patients.

The three exercise arms (isocaloric) are composed as follows:

Endurance training (n=15): 31min at 65-75% HRmax; HIT (n=15): 4x4min intervals at 85-95% HRmax divided by 3x3min of active recovery at 60-70% HRmax, making it a total of 25min; Pyramids (n=15): One Pyramid consists of 8 one-minute blocks. Those are grouped starting with one block of 70-75% HRmax, followed by one block at 75-80% HRmax and another one at 80-85% HRmax. The top of the pyramid are 2 blocks of 85-90% HRmax. Intensity is lowered afterwards with one block at 80-85% HRmax, followed by one block at 75-80% HRmax and last one at 70-75% HRmax. Two more pyramids follow, each divided by 2min of active recovery at 65-70% HRmax, making it a total of 28min.

All protocols are initiated by 5min of warm-up and end with 5min of cool-down, both at 60-70% HRpeak.

Primary Outcome: Individual maximum power output in watt (Pmax). Secondary Outcome: Change of power output in watt at lactate thresholds at 2 and 4 mmol/l.

Inclusion Criteria:

At least one of the following diagnoses within the previous 3 months:

• acute coronary syndrome (STEMI)
• acute coronary syndrome (NSTEMI)
• aortocoronary bypass surgery
• PCI
• stable coronary heart disease

Exclusion Criteria:

• Unstable angina pectoris
• Heart failure (NYHA IV)
• Acute endomyocarditis or other acute infections
• Pulmonary artery embolism or phlebothrombosis within the previous 6 months
• Hemodynamically unstable arrhythmia
• Hypertrophic cardiomyopathy
• participation in another study within the previous 6 months
• Medical conditions which prevent patients from complying with the exercise program