The aim of the present study is to evaluate differential lactate removal kinetics in heart failure patients that are trained according to 2 different exercise protocols:

(A) High intensity intervals training (HIT); (B) Continuous moderate aerobic training (MAT)

Introduction: Congestive heart failure (CHF) patients suffer from early fatigue and functional aerobic impairment. Their reduced cardiac output and O2 delivery to the peripheral muscles shifts those patients consistent anaerobic metabolism, thus, CHF patients rely on anaerobic metabolism even in everyday life activity. This metabolism leads to a shift of muscles fiber types from mainly slow twitch, oxidative type I fibers to fast twitch, glycolytic type IIb fibers. Monocarboxylate proteins MCT1 and MCT4 transport lactate crosses the membrane. MCT1 is responsible for the lactate uptake and MCT4 is responsible for efflux of excess lactate. Exercise training is known to improve the quality of life in CHF. We hypothesized that exercise training might change MCT1 and 4 expression and distribution. Accordingly, these changes may also affect lactate clearance during recovery, which may contribute to the beneficial effect of exercise training in CHF patients. Methods: New-York Heart association (NYHA) class II-III CHF patients will be assigned to the experiment. At baseline and upon training conclusion they will undergo the same tests battery. The test battery includes heart rate, blood pressure measurements, echocardiographic evaluation. All participants will fill out "Minnesota living with heart failure" questionnaire. Subsequently, after their basal blood lactate will be assessed they will undergo measurement which will be followed by lactate clearance-rate evaluation.

Randomly each patient will then be assigned to one of two experimental training groups: (A) High intensity intervals training (HIT); (B) Continuous moderate aerobic training (MAT). Each volunteer will be trained twice a week for 12 weeks, according to his/hers assigned training protocol and in accordance to exercise training guidelines.

Inclusion Criteria:

• Stable heart failure patients referred to exercise training in a tertiary care cardiac rehabilitation institute
• Age > 21

Exclusion Criteria:

• Severe symptomatic heart failure
• Severe orthopedic limitations
• Unstable arrythmia
• Cognitive decline or substance abuse
• Unable to comply with exercise protocol
• Significant pulmonary disease
• NYHA 4 heart failure class